Generally, you’ll need to share a lane with other people. If you’re lucky and it’s quiet you may be alone!
In many pools, lanes are marked slow, medium or fast. Before getting in, take a look at the people already in each one and see which one seems most like your speed. Then join that one. If it turns out you’re too fast for the slow lane, you can always move, or if the medium lane gets too quick, move into the slow lane, etc.
The biggest thing with swimming with others is to be aware and considerate. Swim in the direction indicated at the bottom of the lane: generally up one side, and back the other. If there are others in the lane, join with them. If someone is catching you up, then wait at the next wall and let them
pass. Similarly, if you’re catching someone, you can gently tap their feet (once only!) to let them know you’re behind them, and they should stop at the next wall to let you pass. Some pools allow overtaking, in which case you should swim in the middle of the lane until you’ve passed the person out.
Hat & goggles depends on the pool. Some require a hat, some don’t. I’d recommend goggles just because I think it makes it easier, you don’t need to worry about splashes etc.
I’ve found mid morning and mid afternoon is often quietest. There’s often a bit of a rush pre-work, at lunchtime, and then after work.
Above all, enjoy it!