(NOUN/Plain-Form VERB) + だけで as “just with NOUN/just by VERBing”
The particle だけ which translates to “just, only” can be used not only by itself after a NOUN word to mean “just NOUN” but also together with the particle and instrument marker で after a NOUN word or a VERB in its Plain-Form to mean “just with NOUN” or “just by VERBing” respectively. This grammar pattern is commonly used to describe a subsequent verb clause or simply followed by adjectives such as いい and 十分 (じゅうぶん) to evoke the meaning of “(just NOUN/just VERBing) is enough/fine.”
Kono kikai wa, nejimawashi dake de tsukureru.
You can put together this machine with just a screwdriver.
Kanojyo wa jibun de benkyou shita dake de, ii seiseki o totta.
She got a good grade just by studying on her own.
Ichimai no piza o chuumon suru dake de jyuubun da.
Ordering just one pizza is fine.