A cryptocurrency wallet address is a string of letters and numbers that represent a virtual wallet that you can send and receive cryptocurrency through. Each wallet address is unique akin to an email address and is has specific allocation on the blockchain.
You can think if it as an account number if you were comparing it to a particular bank, and within that bank you have multiple accounts for multiple currencies (USD, EUR, GBP, AUD etc). In a similar fashion, you can have a wallet address for BTC (Bitcoin), ETH (Ethereum) and any other type of cryptocurrency. Staying with the bank analogy, each bank will have particular account numbers for the particular currency and the same is for crypto. If you were to transfer say BTC from another exchange to CoinMetro, you would need to first find out your BTC wallet address from CoinMetro and use that as your destination.
Note: It is extremely important that you copy the address (do not try and type it yourself), and secondly, make sure you have the correct wallet for the correct token (BTC wallet for BTC, ETH wallet for ETH etc) as you cannot transfer say BTC to a ETH wallet.