A 5 for 1 stock split means you will receive 5 post-split shares in exchange for each share you own.
For example: If you owned 20 shares of TSLA on Friday, August 28, 2020 (record date), these shares would be exchanged for 100 post-split TSLA shares which would begin trading on August 31, 2020 (ex-date). The post-split shares should appear in your account before the market opens on August 31, 2020.