What will happen if I buy the same stock at a different price?

You'll just have a larger position, and the computed price paid will either move up or down.

It helps you keep the average cost low and is a technique value investors bullish on certain stocks employ.

It is difficult to predict stock price movement in the short-term, but long-term investors resort to average costing.

Savvy investors buy stocks in tranches for 2-3 months or longer, so buying the same stock at different prices, the average cost remains low.

It's pretty cumbersome to calculate gains and losses yourself, but the app or brokerage firm you use should calculate it for you.

Nothing really, you are simply adding more positions to your trades.

This is common to trading. When we are expecting bullish to move to a certain level, we buy more positions.

I strongly advise you to do this only when your analysis of a certain market is suggesting higher prices.

Else, simply leave only your current position in to run as far as you are comfortable with.