An ETF is an investment fund made up of stocks from different companies. A fund based on electric vehicle market could include Tesla, Chevrolet, Toyota, Ford, Kia and various other companies building EV parts like BASF or Northvolt for batteries or chargers.
The fund could be composed of, say, 30% Tesla, 10% Chevrolet, 10% Kia, 5% Ford, etc.
You can invest in the fund by purchasing parts, which then give you a return based on how many parts you bought and the performance of the stocks in the fund.