Zoom the camera in towards the structure - makes the structure bigger.
Switch to the next frame, or the first frame if all frames are currently visible.
A "frame" means different things depending on what type of data is being viewed. If the structure is a single MMDB entry, but is for example an NMR solution where the original PDB entry contains multiple models, then each frame will contain one model. If it's a single structure, but the PDB entry has disordered residues, then each frame will contain one ensemble of disordered coordinates. If you're viewing a multiple-structure file (like a CDD or a VAST alignment), then each frame contains a separate PDB structure.
There are two different types of animation available: frames and spinning. Play frames will flip through the frames without moving the structure, whereas Spin will continuously rotate the current structure. Stop will discontinue either type of animation. Set delay allows you to specify the time - in milliseconds - spent on each frame (and so applies to frame animation only); a smaller value will make the animation go faster.