Can someone please explain this to me?

I had a lot of viruses on my computer, so I had hard drive cleaned up at a store. When I got it back home, it needed one more thing to fix it. So, the store owner said I had a Tab open, and that I had a lot of Tabs open when I first brought it to him. He closed the Tab, and I took it home. I used the computer, and when I went to my emails, they were all gone! I thought he had deleted them, which I wanted to keep for personal reasons. But, somehow, I found all of them in Outlook Express! I don't know how to use that program, but I'll leave the emails in there anyway, so long as I know where the emails are. I saved some emails last night in Yahoo, and this a.m., when I went back to them, all the emails were gone. I checked Outlook Express, and they weren't there, either, this time. I don't know where they went. What I would like explained to me is the Tab the man closed that sent all Yahoo emails to Outlook Express emails. I have never heard of Tabs before, and that you have to close them. So, I don't know how to close them, or where they are, either. I am not very good with computer Lingo, so please explain what is going on and about the Tabs, in plain English. And, since the man closed the Tab, where are my emails going now? Thanks!