We can develop a simple 5-step "thought model" or "conceptual model" for an alpine/valley glacier. Label these steps from 1 (first step) to 5 (last step) using numbers only.
1) glacier ice moves downhill under influence of gravity
2) glacier loses mass/ice at the snout or terminus
3) snow compacts and recrystallizes into ice
4) glacier moves into the "zone of ablation"
5) snow falls on the head or upper part of the glacier.