The terms “pinfall or submission” are simply the means by which a competitor can be deemed the winner. In every match, there will be certain stipulations. Stipulations indicate what weapons are considered legal (like a TLC match), or how a person may win the bout. “Pinfall” refers to your classic 3-count style pin-match.
Pinfall
The competitors can go about beating each other down by any legal means. That is, unless other stipulations are set, such as no-disqualification, etc. But, the only way to win is by “pinning” the opponent for the referees’ count of three.
Submission
“Submission” is the other classic win-method. For submission, a competitor must get the opponent in a hold and get them to “tap-out.” The tap-out is exactly that.
When the opponent cannot take the pressure of the hold any longer, they will signal that they are forfeiting the match. In some cases, the opponent does not tap-out, but is considered a tap-out say, for example, if they actually pass out and cannot continue.