If something or someone penetrates a physical object or an area, they succeed in getting into it or passing through it.

If someone penetrates an organization, a group, or a profession, they succeed in entering it although it is difficult to do so.

If someone penetrates an enemy group or a rival organization, they succeed in joining it in order to get information or cause trouble.

If a company or country penetrates a market or area, they succeed in selling their products there.

If you penetrate something that is difficult to understand, you succeed in understanding it.