NewTrader ...
When any public company moves to buy another, you will first hear of the action through the press, then somewhat later you will be formally advised by your broker. A share buyout price will be identified by your broker, and if you like the price, you can phone them and put in a SELL order.
In many, many cases, however, the market upon hearing of the bid will immediately "price" the equity. If the market price is higher than the bid/takeout price, then the market thinks that there may be another potential purchaser. And a bidding war may begin.
(If the action goes like BCE, where the market price is lower than the bid price, then everyone gets really confused. Fortunately, I don't have any BCE shares.)
If you have a full service broker you could ask for advice; if you are investing through a discount broker, you might be advised to stay in touch with your friends on the Agoracom boards. Naturlaly, you can sell or buy at any time. Due diligence is always, always required. The Agoracom boards are generally very good at helping you get your DD.
Snug