By default, when you click a cell in Excel and hit Ctrl+B or the B button on the toolbar, the entire text of the cell becomes bold. However, sometimes you may want to make just part of the text bold, and not the whole thing.

To do this, simply start editing the cell by hitting F2. Select the text you'd like to make bold, and hit Ctrl+B. This will make only this part of the cell bold.

You can use this same technique to color specific words in the cell: Select one or two words while editing a cell, and use the Font Color button to change their colour.

Source: How to make only part of a cell bold in Microsoft Excel

Not tested for Excel 2010 but I think it should work.