You can resize it horizontally and vertically (but not diagonally). So if you go to the edge and grab the line, you should be able to stretch it out in either of those directions.
To draw a simple line, hold down the L key on your keyboard and drag out the line. Then, when you have the line selected, you can use the properties bar to change the line style, shape, etc.
Containers are designed primarily for separating content, so you can't add text directly into the container. However, you can add a text inside of the container, which will allow you to add text.