Some basic chess.com questions

What does the rating # in parenthesis  on the Tactics trainer page displayed after you solve a tactic mean? 

It is the puzzle #

Thanks.  Does it reflect the difficulty order or is it just randomly assigned?

They are numerically assigned when loaded into the system. You can see that by looking at the following page:

https://www.chess.com/tactics/problems?sortBy=sequential

Plus, ratings change on tactics when they are solved/failed so even if they had been loaded in initial rating order, they wouldn't stay that way.

Next question, do I get a rating from playing the computer or do I have to play actual people?  I am so bad I'm afraid to play anyone.

The Play vs Computer in Play > Computer is not rated. You can play the Computer Players in Live, those can be rated:

@computer1-easy

@computer2-medium

@computer3-hard

@computer4-impossible

They often have open seeks and I believe you can directly challenge them.

When you play another person is there some sort of side channel communication or is the only interface the board?

There is a chat option if both players have it on.

Returning to Tactics Trainer, I am being fed very low rated puzzles and yet it's telling me that only 60% of those presented with them got them.  How can this be?  I didn't think anybody else was as bad as me.  Am I reading that percentage correctly?  

Yeah, you're probably reading it correctly. 60-70% is pretty average for 400 rated puzzles (just look at the first page of 400's)

https://www.chess.com/tactics/problems

The system gives easy problems to new players and harder ones to more experienced ones, the percentages hover around 50% for this reason.

It also means that these percentages are completely meaningless.

Thanks for answering my questions!

While you can play the computer at various levels, computer play is simply, well, inhuman.  Even at lower levels, it just doesn't play like a human player does.  It doesn't make the same kinds of mistakes.

If you play a human player and lose, your rating will go down.  After a few games, it will start to settle around your true level, and the system will tend to match you against people at about your level.  So you won't generally get trounced by players five hundred points above you, and you won't get to beat up on players rated 500 points below you.

If you're having fun and playing fair, it doesn't matter if your rating is 700, 1700, or 2700.