I won a match?
Okay, I'll admit I haven't a clue how this works. Even after it was explained to me, I still can't figure out how to change my roster and the rules pages are as impenetrable as the bible and possible longer.
Indeed, you are 2-4, soon to be 2-5.
OK, let me try to 'splain this.
On your roster page, you have the active positions (QB, RB, team DEF, etc.) and six bench (BN) positions. If you are using the drag & drop interface, you drag the little blue box for the bench player and drop it on the box for the guy in the line-up you are replacing. These must be position for position; that is, you can only place your active QB with another QB. (The exception is the W/R/T position, which can be a WR, RB, or TE at your option.) The player you are replacing goes to your bench and is still in your possession.
Reasons for substituting: starting player is on a bye week, starting player is injured enough to miss a week (but not out for the season), you think the bench player has a better match-up.
Now, what if you need to sub out your QB but don't have a QB to replace him with? That's where waiver wire pickups come in. When you're looking at your roster page, up near the top is "Players: Add." That'll give you a list of all available players. You can use the "position" drop-down to filter on the position you're looking for, and the different columns to sort by stats ("Actual rankings" is useful, as are % owned, total fantasy points, and in some cases yards gained, receptions, what have you. The default ranking is "projected ranking" which is completely useless at this point in the season).
When you find the guy you want, click the green plus sign to pick him up, but then you will be asked who you want to let go. This does NOT have to match the position--you can pick up a QB, and drop any player you wish to make room for him. The player you drop will go back into the pool, and any other team can pick him up. So before you drop a guy, you'd best be sure you won't want him back later. Certain guys you are not allowed to cut; they tend to be the big stars (mine are Manning, Peterson, and Antonio Gates) so you don't want to drop them anyway.
All waiver wire claims are subject to the waiver wire pecking order from Monday to Wednesday. That is, if you try to pick up a guy on Monday or Tuesday, it won't be processed right away. If more than one team tries to claim the same guy, on Wednesday morning he'll go to whichever team has the better waiver order priority (which is visible in the standings table, but I have no idea how it's determined). From Wednesday through Sunday, it's open season, and whoever you pick up will go on your roster immediately.
Reasons for picking up a guy off the waiver wire: starting player is on the bye week and you have no one available on your bench. Starting player is injured and out for the season. You have realized the guy you have sucks and is irredeemable, and there has to be someone better out there. You have heard of some great new player who's come out of nowhere and you want to pick him up.
Does that help? Other questions?