Hmmmm.
Read the manual, may not have been a helpful comment. Its not the easiest manual to read, but I promise you the more time you spend reading it and working with mikrotik you will get used to it, and so yes, you should read the manual because all the answers are in there.
But as this is the Beginners Forum I will put a bit more info for you.
OK, Lets start:
First off you have traffic passing through your router. Now you want to mess about with that traffic and do things like manage bandwidth and set priority.
So if you learn one lesson today learn this one.
If you want to fiddle around with traffic in Mikrotik it means that you must identfy that traffic that you want to play with first. We call this MANGLE. Read about that in the manual. MANGLE means to MARK the traffic, or identify it and place a mark on it so that you can do stuff to it later.
you will use MANGLE VERY often in mikrotik so get used to it. You find it in the IP FIREWALL MANGLE menu.
Now you have marked your traffic, such as traffic going to x or coming from y or perhaps traffic that is web or traffic that is ftp.
Now it is marked or mangled you can start to mess with it. This is what queues (and other things) are for.
So you must take the marked traffic, (lets say you marked traffic as WEB and ALL OTHER) and place it in a queue where you can now set the speed or priority or both.
Ok, there is some back ground, now you need to read the manual and also refer to the wiki where you will find examples to paly with.
http://wiki.mikrotik.com
Well, good luck!