Hello everyone,
It's not been a long time since I discovered Bitcoin and it fascinated me. I have created wallets online and with some software. I need help with some things though.
First of all, welcome to the fascinating world of bitcoin!! 
Should I use an online or a software wallet? I have searched around and people say that software wallets are much better.
Largely depends. If your only planning on holding a small amount of bitcoin in order to play around with it and perhaps make a couple of small purchases then some sort of web-wallet like blockchain.info will likely suit your needs just fine. If however, your looking to invest a decent amount of fiat into bitcoin and hold it safely, a hard wallet like Trezor highly recommended. Also, if you decide to run a full-node (best option overall but resource intensive), you have the dual benefit of a wallet that actually downloads and works on the entire chain and supporting the network at the same time 
How can i add funds to the wallet you will suggest? I tried adding funds on Blockchain but it won't accept my credit card. I live in Greece if that makes any difference.
Given that you live in Greece I would strongly recommend going with an established service like https://www.coinbase.com/join/514ae1456770d04c83000025. They allow purchasing and selling of bitcoin via ACH deposit to bank accounts, and now even Paypal.That's about it. Thank you for your answers!
My pleasure. Best of luck to you 