How do you not suck at this game?

If I were to give you just a single tip, it would be that the key to the game is raw production.  Each unit of production yields one unit of social production, one of ship production, one of research, and one income.  So build up your raw production by increasing your population and building bases on asteroids.

Welcome to the community Icedanno1802.  Here's some suggestions.
Start a new game with non-default conditions

- try it with a large galaxy to give you some more room

-set the number of opponents to be lower, maybe 3 or 4?

- set the game level to easy

- Play as the default humans

Once you're in game, some things to try

- be willing to redesign ships (the functional bits) to use that new tech and optimize for cost

- you need to explore and find new planets to colonize

- you need to research movement tech up front, and maybe life support/scanning tech as well to make your exploration better

- take advantage of improvements on advanced tiles and neighboring bonuses

-raw production is critical each 1 raw is +manufacturing, +1 science and +1 cash

- building a factory right next to the planet capitol is a +1 to raw, so is 1 more population

Try that, and see if it helps

I think it's the asteroids. It's not a very obvious aspect of the game, yet it's so crucial for production.

Thanks for the tips.  I've spent quite a bit of time looking at the advice on other sites, and I think I have a sorta ok handle on the game.

Trouble is, EVERY game ends the same way.  Someone declares war on me, and then sends in fleets to wipe me out.  Takes me 6 or so turns to crank out one Medium ship, and they have several FLEETS of ships, all with better weapons, defences, etc.   

Fun game up to that point, but then it just turns into a wasted afternoon.  What is the magic button I'm not pressing here?!?!?!

You playing Crusade or above?

5 Planets to a shipyard.

Hubs are Key. Flat bonus building surrounded by the same or % based if not. (Space Elevator, Captial are 2 center Hub buildings)

Economy Starbases, thier bonuses stack.

Specialize planets, you only really need 1 Mega research world on small - mendium maps the rest should be Manufacturing\Economy.

Big maps. The computer on small maps is super aggressive and damn quick. If your computer can handle it the bigger the map the better. I don’t like to see an AI till turn 75 to 100. I played on the second largest map with only 7 opponents otherwise my computer starts to trip out at the late game. This allows for some empire building also the computer normally won’t declare while expanding or if they can’t reach you. Also while learning there is no reason not to turn the difficulty down. This is one of those games where normal is a bit hard to learn the game. 

Welcome to the community.

Ah, ok as noted above you need shipyards that can produce ships, and that implies up to 5 planets contributing to each shipyard. If the planets you own aren't in the same system, they won't automatically add to production- you have to manually add planet sponsors from the shipyard menu. Distance matters as the amount of shipyard production is limited by distance

Also, don't overlook the value of fleets of smaller ships- 3 or 4 tiny ships combined can be much more effective than a single medium.

If you're seriously looking for help and not just here to gripe, please post exactly what expansions and DLCs you have, what civs you have tried playing, whether you're playing campaigns or sandbox games, what techs you typically research in what order, and whether you pay attention to adjacency bonuses when building out your planets.  Maybe then we can post some more specific advice. 

Your personality will help decide your stratagy.

For me a little of everything seems to be best.