We're just simple enlisted men in the Time Wars.

Jo is not aware of the Time War which destroyed The Doctor's people.

The Doctor doesn't mention the Time War at all to Jo.

The Time War concluded with the mutual destruction of both belligerents and their respective planets.

What happened to him after that, is yet to be established; but he is assumed to have been killed in the Time War.

The Doctor makes reference to having to end the Time War.

This is the first mention of the Time War, which would be one of the running threads throughout the series.

It also seems to show that she survived the Time War.

However, instead of killing him he teamed up with him and participated in the Time Wars.

Whether she had survived the Time War or if she was not even a part of it is also unknown.