figurative form of speech.
It means If you understand what a person is implying or follow where they're getting at in a conversation.

Usually substituted for the following phrases:
"If you know what I'm saying." or "If you see what I mean."

If you get what iam saying

If you understand what i mean/ direction of my thoughts (if you follow my train of thought)

If you understand what I mean, often in reference to the rude version of a double entendre or innuendo.

do you understand the words that are comming out of my mouth?

The worst phrase to have ever fucking existed.
If you say this you probably cheated on your girlfriend with your sister and smell like doritos.

The stupidest fucking phrase to have ever existed.
If you say this phrase you most likely chested on your girlfriend with your sister and eat doritos for breakfast.