Here is an activity diagram example for ATM.
Withdraw money from an ATM Account - The three involved classes (people, etc.) of the activity are Customer, ATM, and Bank. represented swimlanes that determine which object is responsible for which activity. The process begins at the black start circle at the top and ends at the concentric white/black stop circles at the bottom. The activities are rounded rectangles.
A single transition comes out of each activity, connecting it to the next activity, which may branch into two or more mutually exclusive transitions. Guard expressions (inside [ ]) label the transitions coming out of a branch. A branch and its subsequent merge marking the end of the branch appear in the diagram as hollow diamonds. A transition may fork into two or more parallel activities. The fork and the subsequent join of the threads coming out of the fork appear in the diagram as solid bars.