why can't i finish a game

Chess is "hard" because it was designed to be "hard".

Have you studied the basic checkmates? That is probably a good place to start:

King and Rook

• Use your Rook to limit where the opponent's King can go.
• Always keep your King 1 rank or file in front of your King.
• Do not place your King and your Rook on the same rank or file. This will give your opponent's King an escape route and you will have to start all over quarantining it.
• When your opponent positions his King in front of your King (and it is safe to do so), drop your Rook. This will force your opponent's King further back.
• Always keep your Rook at a safe distance from you're opponent's King.
• Remember that it's your opponent's job to place his King in front of your King. In a scenario where moving your King places your King further away from your opponent's King or in front of your King, make a small "counting move" with your rook to force your opponent to move again.
• When your opponent's King is on the edge of the board and can not move back a rank, Checkmate is achieved.

King an Queen

• You may always use the King/Rook method of checkmating an opponent when you have a King and Queen.
• The King and Queen method is faster.
• Remember that Queens defend not only ranks and files, but diagonals as well. It is easy to stalemate your opponent when a King and Queen face off against a lone King.
• Always allow the opponent's King a place to flee from check until you are ready to achieve checkmate.
• Use your King to defend your Queen.
• Use the Queen to limit where the opponent's King can go.
• When your King is one square away from your opponent's King, and it is safe to do so without causing a stalemate, place your Queen between the two Kings.
• When your opponent's King is on the edge of the board and one square away from your King with the Queen in between the two Kings, checkmate is achieved.

Two Bishops Checkmate

I don't have this one figured out by a long shot; it's a tough one!

https://www.youtube.com/watch?v=uimbIq9h_7A

• Keep your Bishops out of reach of the King.
• Bishops, when side by side, protect each other from the King advancing close enough to attck them.
• Position your Bishops so that they control the 4 central squares of the board.
• Occupy the center of the board with your Bishops. This limits your opponent's King to just 12 squares.
• Move your King one square away and on a diagonal of one of your Bishops. This will force the King further back.
• Once in position, advance your Bishops  one rank, side by side. Always move the Bishop furthest away from the King.
• In pushing your opponent's King further back, make sure that you allow the opponent's King a place to go.
• Make waiting moves without surrending control of squares when necessary.
• The King will be forced to the edge or corner of the board where checkmate can be achieved.

Then there is the "Bishop/Knight" checkmate; probably the hardest of all; which I haven't even began to figure out!

Please keep in mind that these puzzles were designed by someone who isn't much further along than you; but hopefully, these modest puzzles may give you a bit of a boost.

I'm going to go take a look at some of your games now ...

1. Forget about openings.  As youre finding out, knowing openings doesnt mean squat at your level.  

2. Learn and understand Opening Principles:

a. Control the center.

b. Develop minor pieces toward the center.

c. Castle.

d. Connect your rooks.

3. Tactics...tactics...tactics...

4. Basic mates:

a. KQ vs. K

b. KRR vs. K

c. KR vs. K

5. Basic King and Pawn endings:

a. KP vs. K

b. Opposition.

Checkmate with 2 Bishops is harder than the King and Queen and the King and Rook Checkmates.