だけで is a combination of the 副助詞（ふくじょし） (adverbial particle)
だけ, and the 格助詞（かくじょし） (case-marking particle)
で. This expression is regularly thought of as meaning ‘just by (A), (B)’. However, the literal translation is a bit closer to ‘with only (A), (B)’. This reflects the
で particle’s standard usage of showing a ‘tool’ that is being used to achieve a certain result.
To use
だけで, simply attach it to the end of any (non ます) form of verb, or noun.
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彼女（かのじょ）と話（はな）すだけで楽（たの）しい。
Just talking with my girlfriend is fun. (We don’t need to do anything else, because talking is fun enough)
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これは電子（でんし）レンジだけでオーブンの機能（きのう）はついていない。
This is just a microwave, an oven function is not included.
だけ differs from しか in one very important way. だけ highlights that there is/was more than one option, but that only one thing was chosen/used. However, しか implies that there is only one possible option to begin with.