How to analyse a board position for the best next moves

How do I get chess.com or another program to analyse from a given board position what are next few moves that are best for white and black to continue the game? 

That is exactly what a chess engine does by definition.

Okay. What tab or button in chess com site takes me to a screen where I can set up a board and ask the chess engine to show the next handful of moves that assume both players are taking the best moves. 

chess.com doesn't have one, use a chess engine.

How do I find online or buy a chess engine?

Stockfish is free and extremely strong, start there.

He's pretty clear in what he's asking about

Chess engines are a tool that help analysis and you can't rely on them because of the 'Horizon effect'.

In my opinion it's best to learn how to analyze by studying annotated games by grandmasters. And it really helps to memorize the games too.

When you talk Chess Engine? what are you talking about? it`s some one there, who, explain,?

I think Fritz is a popular one, i bought it from Chessbase.  But it's not straight forward to use. There's a lot of apps available for phones. I use smallfish on iphone . They'll basically suggest the best move in a given position.  I like a lot the chess.com computer analysis. I get it to analyse a lot of games i play here. You can find it in the game window. It'll tell you whether a move was a mistake or a blunder and you can see whether your position got better or worse with each move and a few lines of alternative move.

Engines aren't always accurate.

You can find some positions they calculate wrong, but those positions won't be occurring in your average game.

Chess.com has good post mortem showing inaccuracies and mistakes and blunders -- but all at the end of the game here (or in free Stockfish engine) to view the engine's suggested alternative even as I make the questionable move, or just after, so I learn in real time?

I would not use the computer to tell me what moves to play next against a current opponent. That would not be playing chess that would be the computer playing chess.  I was looking to understand in certain openings how to best capitalize when a counterparty move "leaves the book opening or response" in a way that presents a significant opportunity.

Yes, the mechanical turk, or great chess player automaton. 

i do NOT want the computer to play for me..  After the game the engine lists a few "inaccuracies, mistakes, blunders" from my moves (not interested in my opponent's moves).  These are very instructive as they show up my blindspots.  However it is very time consuming to reconstruct the game to arrive at the few points which triggered engine disapproval.  Would you believe I no longer even own a chess set at home any more.  All games are about mouseclicks and replays.  If the engine's written comments came as popup AFTER I made an inaccurate move, that would be truly helpful.  Game improvement by leaps and bounds I think.  Repeat I do NOT want engine to suggest moves, just to point out inaccurate moves AFTER I have made same, too late to score an advantage over the engine-less opponent. 

"not interested in my opponents moves"? Whaaat?  Good luck with that bubber...

In the limited time available my priority is not to review opponent's mistakes, most already recognised.  s23bog you are pompous garbage.  You are ignored.  Not interested in your pompous garbage.  Walking away from this thread and your ugly moronic exhibition.  Goodbye mr s23bog.  Bog is correct description.  Ugh.

If you dont understand +.4, then chess engines are useless to you.

It's pointless to only look at your position and ignore your opponent's.