Typically, your inbound server is the one used by your mail provider, and your outbound is the one run by your service provider. Eg, you might receive mail from Gmail’s servers but send it through O2’s.
The other way of doing it is to use the email provider’s server for both directions, but the gotcha in doing it this way is that the requirements to do so will be stricter. Depending on the provider, you might have to use a secure connection, or encryption, and will almost certainly have to provide login details.
Step one is to look at your settings. Step two is to check back with your provider to see if they’re correct and meeting all their security requirements.