At the bottom right of your screen you will see a bar, with squares numbered from f1 to f10. This is the Quick Slot Bar or as i call it, the Combat Bar. You can put nearly anything in these bars that you want. I will try to show you the effective way to use them. Now remember, later on, you can change what you want to fit your needs.

Now to put items on there from the inventory or other window, you just drag the icon you want to the bar.

Put the pet pickup icon on F1 square on the bar.
REASON: When you are killing and you get a drop, it is easier to press the f1 key from the keyboard, while you are sighting on your next target. Remember, you only have about 20 seconds or so to pick up your drop. If you do not, then someone else may do so, WITHOUT asking. It is considered a free drop. But be courteous and ask first as generally most of the time people will let you pick up the gold drops. And your drop disappears after 5 minutes. When you are alone and grinding away, you may just kill and then see how much gold you can get on the ground. It looks neat and breaks the boredom too.

Put your herbs on F2 and Stones on F3, when at low levels.
REASON: At low levels, there are monsters that want to hit your pet instead of you. Or you may be fighting two or three horned beasts and one of them is hitting your pet. Sometimes, even at high levels, I let the monster hit my pet instead of me. That way I can survive longer. Anyway, if you are at the horned beasts it is a lot easier to hit the f2 key, versus clicking herbs on your inventory now. You will find it is a lot easier to feed your pets. This is for low levels now. Once you start getting around level 40 or so, you acquire more skills to put on a bar. Remember there are 3 bars. So have one with the herbs and stones on them now.

Put your pet icon on f10
REASON: You want your pet icon present but out of the way. This way you can unequip or equip your pet real fast if you have too. Some monsters hit your pet and you will find that if you quickly unequip your pet then equip it, the monster may direct his attack to you now. This way if your pet is low on food he will not be killed. Remember when you click the herbs to feed your pet, it is not instantaneous at times. That is why you may unequip him real fast then equip pet, to give you time to feed your pet. Sometimes the monsters can hit your pet faster then you can feed it.

If you have a mounted pet, place it on f9 and the Pet Village Return icon on f8
REASON: You always want your pet return icon, next to your pet icon. I have a drake and sometimes I need to get out of Dodge City real fast.(American expression, for getting out of the area real fast) So I click to my mounted horse icon then quickly hit the pet return real quick. This has saved me many a time from getting killed. But if you are killed on a mounted pet, then your pet is dead too. The return is nearly instantaneous.

On one bar, have the pet pickup and manual pickup icons on the same bar.
REASON: Have you been to a monster spawn lately? At the end of each spawn the treasures are put out. The trick is to look and go to the first treasures that are spawned, as these will be the first ones you can pick up now. Now most people use the pet pickup key and then they try to manually pickup with their character. Problem of picking up with your character is it difficult to pick up treasures in a crowd. Now if you put the manual pickup on the combat bar, then you just press the pet pickup and the manual pickup keys rapidly. Your pet will pickup the nearest treasures and you will automatically pickup the nearest treasure, even if you are in a crowd. Then when that group of treasures are gone, your character will go to the closest treasure for pickup. Well there goes one of the easiest secrets out now. Lot of things are here to use, but it is just a matter of using them right. Not all think of this, because when they had the spawns and treasures in the arena, many people were hitting others to try and pick up treasures. I was guilty of that too, till one day I thought of putting the manual pickup on the combat bar.

Designate one bar as your "Combat" bar, for grinding or when in a party.
REASON: You want to have one bar that you will use primarily when your are "grinding" the monsters or are in a party. Remember there are 3 bars now. In my levels from around level 40 plus i had one bar with the pet pickup on f1, skills on f2-f7, pet return on f9 and pet mount on f9 and pet on f10. With my new skill Dash, a level 70 skill, that replaced the pet pickup on f1. Pet pickup went on f8, replacing pet village return. But I can now switch bars fast enough. On Bar 2, i have my horse on f9 and pet village return on f8. So it is easy to switch over fast, especially when the dragon shows up. So you can see that the bars will slowly change as you add new stuff to them as you acquire more skills to use.

Designate one bar as the Grand Red Dragon bar.
REASON: In fighting the GRD or even the Kamira, you need to have the Large Healing pots present on your bar. So when you get hit, then it is easy to click that key designated for the Large healing potion. Depending on your class too, you may have another slot for mana potions too. This is like a combat bar, but no pet pickup, pet village return, and your mount may not be present. Again, this is a matter of skills that you use. A rogue does not have as many skills compared to a Royal Knight. A Royal Knight at level 40, will have his Shield Strike (Stun), Double Bash, Triple Bash, general skills on his bar. Then his buff skills, Devotion, Concentration (Conc), and Divine Shield on the bar. So these are 6 skills that are nearly mandatory to have on the combat bar together. So you can see each class will have a different set up for the combat bar. Now the GRD bar, has to have the large healing potion and possible the large mana potions present. Remember, you can switch to the other bar, with the pet pickup and manual pickup on it now.

You will have the 3d bar, with the manual pickup and pet pickup together and whatever you may deem necessary for you as a player.

Remember these are only guidelines to show you what and how the quick slots or combat bars can be utilized. Hopefully, you may get some ideas from this and learn to use them early in your leveling to be more efficient. Later on at higher levels you will be adjusting the combat bars to fit your style of playing.