Unless you have a Crest account will get a share certificate, and you will need that to sell them when you want to. If it gets lost it's huge hassle. I had some shares a few years ago and wanted to sell them at a peak. I couldn't find the cert for a few days, by which time the peak had passed. It cost me about €200, so it was a valuable lesson.
It's an easy enough process. You just walk into any bank with a share dealing service, put in your order and they put that through to their broker who purchases them. If you do it through your own bank you can fund it from an account, which saves having to carry cash/drafts etc. A cert gets sent out to you a few days later.
To sell them, walk into any bank with the certificate and give your instruction to sell.
Just as an aside - a 2-3 month timescale for an investment in the stock market, particularly with the financial sector which is very volatile is a fair gamble.
Edit: Looking at share prices you may have missed the boat - AIB is up to 8.23 now.