Capital gains tax in Texas - 0%
If you own stock, you don't pay tax on the stock until you sell them. On the day you sell, you have to pay taxes based on how much the stock went up in value, capital gains. You pay capital gains tax to the federal government, and usually, also to the state you are living in on the day you sell the stock.
For example: If you bought $10 of stock, and then sold it for $110, you have a capital gain of $100. If you live in California on the day you sell the stock, you have to pay California $13.30. If you live in Texas on the day you sell the stock, you don't have to pay Texas anything.
(I simplified a ton of stuff above such as ignoring dividends, deductions, etc. It's not all the official rules and details, just a high level introduction.)