。
You can carry out projects that you thought up yourselves.
Literal
Self-[plural-達] [with/by-で] thought-[past-た] project [object-を] execute [thing-こと] [subject-が] can-do-[polite-ます].
~ことができる is the formal 'can do X' construction, combining the nominalizer こと with 出来る ('be possible'). It's a more polite alternative to the simple potential form. 自分達 ('we/ourselves, plural') contrasts with singular 自分. 企画 'project, plan' (not to be confused with 計画 'plan' — 企画 is more about initial conception).