The way this works is that we draft a 25-man roster from players who were on the winning side in the World Series (you cannot draft from a losing side, so that eliminates some all-time greats like Ty Cobb, Ted Williams and Barry Bonds).
For instance, with my first pick I could select Babe Ruth from the 1927 Yankees. Because Ruth only played right field in that World Series, the only place he can play for my team is in right field. If I select Ruth from the 1928 Yankees, I have the option of using him in either left or right field, because he played both positions in the World Series that year. If I select him from the 1916 Red Sox, I can only use him as a pitcher.
With my next pick I could select Pete Rose. If I draft him from the 1975 or 1976 Reds, he can only play third base for my team, since that's the only position he played in those World Series. If I select him from the 1980 Phillies, I can only use him as a first baseman.
Once a player is drafted he's off the board, so if I take Reggie Jackson from the 1973 A's, someone else can't come along and take Jackson from the 1977 Yankees.
Once we've each drafted our 25 players, we'll start a new thread where we can post our rosters, name our teams, set our rotations and batting orders, etc. I'll then arrange a series of head-to-head matchups where each participant gets to vote on which team is the better one, and we'll keep narrowing it down until we have a winner. At this point it doesn't matter which team a player was selected from, because we'll take the players' entire careers into account when judging the teams.
Does that answer your question?