One of the beauties of Reason is that a keyboard MIDI controller isn't necessary to begin creating music within Reason (I'm in the process of building a home studio and won't be able to use any of my ten synths as controller until I get a new computer, still several months away). You can use Reason's piano-roll style sequence editor to write your sequences and its really quite straightforward, although a bit tedious.
Open Reason, create a new file, add a synth, such as Subtractor (a great little analog style synth thats easy to program) and pick or write a sound you like. Right-click on Subtractor > create > sequencer track, then click on the 3-bar button, just above your track editor, to get to the sequencer track (make sure you have the Subtractor track selected). You'll now see a vertical piano keyboard to your left, which you can click on the notes to hear them. You can then write the sequence using the tool buttons above the sequence track (pencil, eraser, selection, etc.)
I'd suggest going online and buying a used book on Reason in order to learn more, as I could fill several screens-worth of tips for you. Reason also has plenty of info in its Help files. But yes, you don't need a MIDI input device at all, to create music in Reason and thats a very beautiful thang. ;-)