By what transport to the destination?
Say 電車で学校へ行きます. Point first to 電車で as the means, then to 学校へ as the endpoint. Replace only 電車 with バス.
1. Transport + で names the means
In 電車で学校へ行きます, the means of transport comes directly before で. That block answers ‘by what means?’. The destination has its own block, 学校へ, and 行きます completes the movement.
Do not swap the roles: 電車へ学校で行きます makes the train the destination and school the means or location, which is not the requested trip. Build means + で first, then destination + へ.
電車で学校へ行きます。
自転車で駅へ行きます。
2. 何で asks for the means of transport
Replace the unknown means of transport with 何 and keep で: 電車で学校へ行きます becomes 何で学校へ行きますか. In this travel context, 何で is read なんで and means ‘by what means/how’.
Elsewhere, informal なんで can also mean ‘why’, but that is not a production target here. The destination and 行きます show that the question expects a mode of travel. An answer can be short: 電車で行きます.
何で学校へ行きますか。
電車で行きます。
3. The role of で follows from the word and verb
Compare three functions here. 学校で勉強します has a place before で; 電車で行きます has a means of transport; みんなで行きます has a group arrangement. The form で is the same, but the relationship differs.
Look first at the word before で and then at the final verb. A place plus an activity gives an action location; a vehicle plus movement gives a means; みんな or 一人 gives the way the group or person acts.
4. 歩いて is the fixed walking form
まで marks the limit ‘up to / as far as’. 駅へ行きます names the station as the destination; 駅まで歩きます says how far you walk. You know まで for a time limit from lesson 12; here the limit is a place. For travelling on foot, this lesson uses the fixed unit 歩いて before 行きます: 駅まで歩いて行きます. Do not add で. 歩きで行きます is not the target pattern.
Learn 歩きます, ‘walk’, and 歩いて行きます, ‘go on foot’, as two available wholes. 歩いて is a te-form. Learn 歩いて行きます as a fixed unit here; this lesson does not derive the general formation rule or ask for new te-forms of other verbs.
駅まで歩きます。
駅まで歩いて行きます。
5. Track each leg separately
Read the existing dialogue about travelling to school. The train belongs to the full school trip, the bicycle to the leg as far as the station, and today 歩いて replaces the bicycle. Note the means and endpoint for each line.
Then create your own fictional route with one means of transport and one walking leg. The final check specifies the intended means and destination each time.