If you do, then go to your local Ukrainian Embassy (Consular Dept.) webite, a Google search should find it and it should provide the relevant information.
There are different rules for different nations but when I was applyinf for Ukrainian visa's I always went for the 'private' rather than 'tourist' visa because one didn't need a letter of invite etc. There was a single or double entry, there was a multiple entry but it was only valid for 6 months.