A private key acts like a password to gain access to a wallet. This should never be given out, as whoever has the private key has access to anything in that wallet. It's important to store your private key securely. It should never be put online, or stored on a mobile phone, or saved in plain text files on a computer. It should also not be given out to anyone representing any kind of support help.
Your private key may look like a long random set of alphanumeric characters. Or, it may take the form of “seed phrases”. These are a series of usually 12 to 24 words in a specific order. Both the seed phrase form, and the alphanumeric forms of private keys can be used to import into a wallet like MetaMask, or even cold storage wallets like Ledger.