If you take a perfective verb like kupić (imperfective would be kupować) and conjugate its non-past stem (the past stem would be kupił), then you get the perfective future tense. It expresses one-time events in the future and focuses on the result, rather than on the process.
The Polish perfective future tense can be translated to English using both future simple and future perfect. It's actually more common to use future simple, since it also often refers to one time events and focuses on the result. In general, there are no exact aspect/tense equivalents between English and Polish.
Because there's a separate construction for that, that also uses the conditional mood.
Conditional mood is based on the Past Tense form, so it shows gender: kupiłbyś/kupiłabyś/kupilibyście/kupiłybyście (masculine/feminine/masculine personal plural/not masculine-personal plural).