What's the difference in meaning between 前にある vs 手前にある?
- 前 means "front/forward" and its antonym is 後ろ (="back/rear").
- 手前 means "relatively nearer position" from the observer (often the speaker), and its antonym is 奥 (="further position", "deep part", "interior").
その店は城の前にある means "The shop is in front of the castle". その店は城の手前にある means "The shop is on the way to the castle" or "The shop is somewhere between us and the castle", and depending on where you say this, it can even refer to a shop at the back of the castle.
When you are talking about a car standing near its back, 前にあるガラス refers to the windshield, and 手前にあるガラス refers to the rear window.
レバーを前に動かせ means "Move the lever forward" (i.e., push), while レバーを手前に動かせ means "Move the lever toward you" (i.e., pull).