To bind a key ingame hit your ~ key. That will bring up your console. Make sure you know the exact name of the action you wish to bind. For example to bind the Fire action to your enter key you would hit ~ to get your console up the enter Bind Enter Fire and that would bind enter to fire.
To practice in single player hit the ~ key and type Start (Map to Load - bridge, fls, hq_raid, insurgent_camp, jrtc_farm, mountain_ambush, mountain_pass, mout_mckenna, pipeline, swamp_raid, tunnel, weapons_cache, leavenworth). For example to start the pipeline map you would type Start Pipeline. Then you need to type Playerlock 0 to allow yourself to move.
In order to practice you need to arm yourself. Hit ~ and type Mpcheat Changeclass (abbreviations for weapon you want), the list of weapons is:
g - M16A2/M203
r - M16A2
s - M82
s24 - M24
ar - M249
m4a1 - M4A1
m4a1auto - Ranger M4A1
ak - AK47
ak74su - AK74
gp -AK w/ launcher
rpk - RPK Light Machine Gun
svd - Dragunov sniper rifle
mos - Mosin-nagant sniper rifle
For example to get the AK47 I would type Mpcheat Changeclass ak. Or to get the M203 I would type Mpcheat Changeclass G. Here's a list of commands you can type to get various results to help your single player experience:
fov X (FOV 90 is default) - To change field of view
slomo X (SLOMO 1 is default) - To change timerate
playersonly - freezes effects, useful for freezing gunfire at height of muzzle flash
setspeed X (1 is default) - To change player speed.
setjumpz X (325 is default) - To change player jump.
mpcheat god - Puts you in god mode.
mpcheat ghost - Puts you in ghost mode.
mpcheat nvg - Gets you night vision goggles.
mpcheat freecamera 1 - 3fd person view, allows free rotation.
fly - Allows you to fly.
walk - Allows you to walk again, but this will screw up stuff like opening doors.
behindview 1/0 - Fixed 3rd person view.
suicide - Kills you.
Also to get some practice dummies type one of these commands in the console:
summon agp_characters.npc_airborneinstructor
summon agp_characters.npc_towerobserver
summon agp_characters.npc_towerobserverfemale
summon agp_characters.npc_flightcrew (Superman!)
summon agp_characters.npc_airbornesoldier
If you're pinging high and getting lots of lag you may need to change your netspeed (especially if you're on 56K). Type Netspeed (Number) in your console. A good netspeed for 56k is 2000 or 2500. For example I would type Netspeed 2500 into my console and it would change to 2500. For broandband users you can easily go up to 8000 or 9000.