You can use it similarly to "via", as well as a place marker. じてんしゃ[で]かよっています - I am going [by/via] bike こうえん[で]あひるがいます - there are ducks [at] the park. Just a side note too, some times you can use へ instead of で, it generally means going in the direction of somewhere, e.g. こうえん[へ]いきます - I am going [towards/to] the park. で is used for a place usually when no travelling is involved.

Particle で has a lot of meaning. I just explain two of them. 1. tool/method(by, with, in) わたしはくるまで行きます。I go by car. 2. place of action (in, at) こうえんでこどもたちがあそんでいます。Children are playing in the park. *be careful that you can't use で for the place of existence or the place of destination. こうえんでこどもたちがいます(incorrect) こうえんでいきます(incorrect) <にほんでいきます>---日本で行きます？日本で生きます？ If you want to say 'somebody goes(行く) to Japan', this is not a correct sentence. If you want to say 'somebody lives(生きる) in Japan',　this is a possible expression although 日本で生活します（にほんでせいかつします） is more frequently used.