If you mean the names of the positions... erm... well...
GK - Goalkeeper. He kinda stands about like a lollypop lady and lets thing past him. But sometimes he stops something, but that's rare.
SB - Side Back. aka a full back, your right and left back. Yeah they usually meander off to the corner flag when the other team attack.
CWP - Central Sweeper. It's like a centre back [see below] but they play attackers onside better.
CB - Centre Back. Although SD for "Saloon Doors" fits them better. When the opposition run at these guys they follow the full backs to the corner flags. Or the decide to join the attack occasionally. They are good at attacking corners mind.
WB - Wing Back. A side midfielder [see below] when there's no full backs. They have no attacking attributes and are only there so that a 5 man defence looks like a "hip and cool" 3 man defence.
SM - Side Midfield. These guys tend to be incredibly weak and are meant to cross the ball in. But they usually drift infield or run the ball out of play. And they don't help defensively. And they go up for corners despite not being able to head it (due to being 2ft high)
DM - Defensive Midfield. Apart from goalkeeper, the most important position as these guys are usually covering when the defenders are out of position ie always. Can't shoot for toffee mind.
CM - Centre Midfield. These guys are "box to box" players. Which means they either cock up the attack and defence alternatively. Don't have stamina, run on 99p batteries from Woolworths you see.
AM - Attacking Midfield. Can be the link between the midfield and attack, but more likely are players who are too weak to go in centre midfield, but can't shoot either.
WF - Wing Forward. These guys are side midfielders who can't cross in the slightest, and are best employed if they play on their wrong foot so they can cut in. Otherwise they cut in and shoot with their wrong foot which is ever so slightly worse than their normal foot. If you have a player who is ONLY a WF (*cough* Burchet) then they are generally useless in all normal formations.
SS - Supporting Striker OR Second Striker. Like a centre forward [see below] who has a higher "Pass Accuracy" than "Shot Accuracy". And erm... they tend to be small, fast and shit.
CF - Centre Forward. These guys will miss all your changes for you.
Attack arrows show where your players will run when your team has the ball. Preferably having all arrows pointing towards their goal is a good start.