im new to Monero, I opened a wallet on mymonero.com and ever since it says you are x number of blocks behind and you have to wait until its complete. my question is can I receive money when it gives me this notification?
If someone sends money to your bank account, you don't have to be standing at an ATM while they send it. They can send it while you're asleep, and you will see it next time you check your balance, even if your local ATM is broken. Monero is the same, except that you can't see your balance while your wallet is lagging — a side effect of the privacy features.
If the person who sent you moneros tells you the Transaction Hash, you can look it up on a blockexplorer, which will confirm the existence of the transaction (but not the amount or the to/from addresses). This works even when your wallet is lagging because moneros are stored on the blockchain, not in wallets. A wallet is just a tool for viewing &/or spending the coins at your address on the blockchain.
You can still receive Monero for your wallet address. It just doesn't show up until it's fully synced with the blockchain. So as long as you get this message you are not in sync with the blockchain but if someone sends you Monero, that transaction will be on the blockchain. You just need to wait in order to see it there.
You just need to open up the wallet and wait until the message disappears. For me, I always get that message when logging in, then it disappears within a few minutes. So open up the wallet, maybe navigate to transactions or something like that, and the message will eventually disappear.