Some scaras are traces left in the sub subconscious mind by our past actions, past language, what we say, and past thoughts. These samscaras become conscious thoughts, or thoughts at the level of the conscious mind. Vriti is a modification of the mind, stuff like a little wave comes upon a lake. A thought, a desire something, maybe anger, maybe resentment, maybe guilt, e various kinds of thoughts. They come up for no good reason at all. And then if you entertain those writtis, ittriti stays on the surface of the mind long enough, it sinks back into themind, into the subconscious mind, and becomes a samscara