The recruitment screen offers you the following actions:
- to specify amounts of infantry/cavalry/artillery for recruitment, using the up and down arrow buttons.
- to recruit a mercenary company, via the same-named button
- to build a conscription center, via the same-named button
- to confirm a recruitment via OK, or to Cancel it, and return to the province screen.
For more information on the costs, limits, etc. of recruitment, see the article on it.