Instead of "forum" can one also use "market"?
You should be able to use "market." Was it rejected? I was given the English to translate and I put, "Marcus ambulare in foro solet." It was marked as incorrect, but it should be accepted, right?
Im confused sometimes is market and then is forum
Is it wrong to use "often" instead of "usually"?
Why not into the forum?
In foro (in with an ablative) specifies a static position (no movement to or from). It simply means "in the forum".
In forum (in with an accusative) would specify a movement into that location, thus meaning "into the forum".