But I don't know how to do that.

Starting a company requires many disciplines, not only in the formation and administration of a real company, but also in solving some of the really hard issues that your company will encounter.  Whether it's how to enter a certain expense into your finances, or even finding a bookkeeper who knows how to do this, or solving a technical hurdle that your technologist just encountered, or whether you're suppose to draft a term sheet first (or let your investors do it), don't think that you have to know all of the answers.  Your first go-to place should be your co-founders and your own database of contacts, then your board, if you have one yet.  These sources will probably have a vast database of contacts, several of which will have your answer, perhaps after one more level of reference to the right person.  Don't hesitate, thinking that they might think you should already know the answer.  Few CEOs and founders can run a company without support.  Tap these resources for your answer and move on to the next challenge.  Now!