You have to supply your own mouse and keyboard with a Mac Mini. The following two tips may be of use if you're coming to a Mac for the first time.
If you're using a non-Apple mouse with a Mac Mini, you may need to install the drivers that came with the mouse. I'm using a Microsoft optical mouse and it was barely usable before I installed the drivers.
If you're using a non-Apple UK keyboard you'll be irritated by some of the keys being swapped round, for example " and @. I installed UK.keylayout from Matt Sephton to map the keys to where I expect them to be. I found I could not unselect the British entry in the International - Input Menu settings so I had to select the new layout by clicking on the input menu on the menu bar (it appears as an icon to the left of the sound icon on the menu bar when you have set the "Show input menu in menu bar" option in the Input Menu settings). I also set the "Use one input source in all documents" option so that once chosen the new layout is used for all applications.