I just found out bitcoin and I chose to use online wallet but there is a fear feel that makes me often check did my bitcoin is still safe. I have read some articles there saying for me to use 2fa as additional security. is that true?
2fa will only confirm that it's you trying to access your account with the service. It doesn't make you 100% sure that the online wallet itself couldn't take your coins like BIT.AC seemingly did, for example.
So it's good for preventing "hackers" through keyloggers and other things to access your online account, but it doesn't keep your coins safe, nor is holding your coins in an online wallet ever going to be particularly safe.
In the case of online wallets that are unlikely to fail with your coins e.g. Green Address, 2fa is a good idea.