Tax implication on short term purchases

I’ve some long term stock ownership and mutual funds and understand the tax implications of selling them well enough.

But I’m struggling a bit with how short term purchases work. I have brokerage account and let’s say 10K I want to just have fun with and do some short buys and sells without actually cashing anything out (assuming I’ll make a profit). Anything I make from a short purchase whould be sold and invested in another stock.

I assume I’ll still need pay short term capital gain taxes. But how is it calculated and I assume the total capital gain is calculated at the of the tax year and any gain from a sold stock over that period is calculated against losses?