A (good/solid/sound/etc.) grasp of/on (something) phrase
"Get" or "have" usually stands in front of this phrase.
A (thorough, wide, sound, etc.) knowledge of a subject, of how sth works, etc.
Before applying for this job, I had already had a solid grasp of what it involves.
Thanks to a sound grasp of English grammar, John has progressed quickly in his writing skills.
Don't rush into doing something advanced before you know the basic skills, techniques and primary details
Don't know anything about something
Don't rush into doing something advanced before you know the basic skills, techniques and primary details
To possess a fundamental degree of competence, intelligence, or common sense
Used to say that someone knows absolutely nothing about something.
The origin of this phrase is not clear.
A group of bad or sinful people
You'd better stay away from them. They are a nest of vipers.