Check your controls. Scroll through the list until you find scouter, set it to a key or button... Change ALL the commands to they're comfotable to you, cuz it's really dumb to keep default key selection in all games.
As for melee: Press number 1 (unless you changed key command), find a person and aim the crosshair at them, press primary attack and when a red box is around them, you're ready to attack. To attack, press primary and you will begin to rush at your opponent, during which time you need to press secondary attack (right-click by default... bad setting if you ask me). When you get close to your opponent, you will hit them. If you made a direct hit, they'll fly off into the distance. However, smart opponents will block, so keep your wits about you and do somthing to get away if they do block.
Now, most people will try to do the same thing to you, so you gotta know how to defend against melee. Check your controls for the block command, be sure to put it in a handy spot. A good spot is usually near your movement keys. When you see somebody comin at ya, press block and wait for them to come at you. When they hit (you'll know when, you'll hear a "smack" sound and you'll lose a little bit of health), you should let go of block and try to hit back (press secondary fire with melee). They won't have time to block, they'll most likely zanzoken away, depribing you of your quick counter.
It takes a bit of practice... Try and find a n00b friendly server, or with only 1 or 2 people in it who don't mind showin you the ropes...... Or download Ki Bot, come back here to ask how to install/work them, and you'll be set