For 'standard' transitions to work, you need 'handles' ... which is tough enough to explain before language/translation issues. But it's the extra frames of a clip that you have 'cut' and don't show on the timeline.
You need to have 'extra' frames of the clip, past the areas where it is showing in the timeline. The transition plays the "outgoing" clip's "handles" over top of the incoming clip's "handles".
So if you need to have say a half second of transition, then you need a half second of unused frames for each clip. So if you move the end edit point of clip A in 15 frames, move the in edit point of clip B back 15 frames, and butt them together, you can now have a 15 frame transition.