You need two books:
1. A basic endgame book like Pandolfini's Endgame Course, so you know how to check mate when you reach the end with a material advantage.
2. A book on tactics. Almost any tactics book will work, but read the reviews to make sure it is not too difficult and has many diagrams to solve.
People our level make blunders all the time, and win by catching the other player's blunders. Once we get better and play tougher players, it is like climbing a hill on a bicycle, and you need to put it into low gear: play for squares and positional improvement to take your opponent one small sliver at a time. But save that for later.
And I just read the other guy's reply. Do not study openings yet. Memorization will not help if your opponent leaves book right away. You will know he/she did not make a grandmaster move, but it still might be a strong move you can't punish easily. First learn tactics. Only after you are good at them can you try to understand the opening at all. Don't be afraid to lose several games in the opening. That is another way to learn tactics.
I am older player 50's - I would like to see my rating go up.
Question 1: What reading material would you recommend?
Question 2: What is the best learning site (besides www.chess.com)?
Question 3: What is the best Chess engine (?) to evaluate finished games or specific game situations?
I know question 3 could help someone CHEAT. I don't get the cheating thing. No cheating here - promise! :-)