Some examples of a beveled cube:

You can access the bevel tool by pressing 'W' while in edit mode (select an object and press TAB)
Once you've pressed W, move your courser farther away from the object for a more pronounced bevel. Clicking will confirm the bevel action.
After you've clicked, you can edit the properties of the bevel in the toolbox window (shown below):

Keep in mind that any further change to the model will cause those setting to disappear, because once you continue working on the model, the bevel will be considered 'finalized'.