'To' means 'with' in the sense of 'I played a game with my sister' (妹とゲームをした。) or 'I ate lunch with my friends' (友達と昼ご飯を食べた). That's why in my previous post, I explained it as 'and'. 'To' does not mean 'by means of.'
'De' can mean 'at [someplace]' but it can also mean 'by means of' as you already know for transportation (see
Denshi Jisho - Online Japanese dictionary.
'De' can be used in multiple other situations.
e.g. 鉛筆
で書いてください Please write
in pen
バス
で行く to go by bus
寝不足
で病気になる to get sick
because/due to of lack of sleep
...not to mention a billion different usages I have yet to learn
ところで、日本語はどこで学びますか。By the way, where to you learn Japanese?