I was playing a game with some friends and I played a Mosswort Bridge and whiffed, hitting all lands. But then I noticed that Mosswort Bridge lets you play a card without paying its mana cost so could I still put a land under the Mosswort Bridge and play it when the conditions are fulfilled?
In m10 they use this convention: you activate ability, cast spell and play lands
So from mtg rules
305.1. A player who has priority may play a land card from his or her hand during a main phase of his or her turn when the stack is empty. Playing a land is a special action; it doesn’t use the stack (see rule 115). Rather, the player simply puts the land onto the battlefield. Since the land doesn’t go on the stack, it is never a spell, and players can’t respond to it with instants or activated abilities.
305.2. A player can normally play one land during his or her turn; however, continuous effects may increase this number.
305.2a To determine whether a player can play a land, compare the number of lands the player can play this turn with the number of lands he or she has already played this turn (including lands played as special actions and lands played during the resolution of spells and abilities). If the number of lands the player can play is greater, the play is legal.
305.2b A player can’t play a land, for any reason, if the number of lands the player can play this turn is equal to or less than the number of lands he or she has already played this turn. Ignore any part of an effect that instructs a player to do so.
305.3. A player can’t play a land, for any reason, if it isn’t his or her turn. Ignore any part of an effect that instructs a player to do so.
305.4. Effects may also allow players to “put” lands onto the battlefield. This isn’t the same as “playing a land” and doesn’t count as a land played during the current turn.
So yes, you can choose a land and you can play it. But it counts for the maximum amount of land played during a turn, because it's say that you play the land and not put it on the battlefield