Knocking sound

Theres rattling sound underneth the car

I haven't had a car for five years.
My family scraped together the funds to do this for me.
I think of the car I own is really my families car.
I planned to keep the good conditions.
I did every oil change on time reasonably.
I hear a knock in the engine.
I went to the smog shop later that day to get smog.
The smog man tells me to get new spark plugs.
The man pushes the spark plug and the engine knock stops.
Is it okay to drive?
Should it stay in the driveway until I can pay for spark plug replacement?
Did I hurt my car by looking for work a whole day?
Should I use a treatment engine additive or special oil?
What do you recommend?

Engine knocks loudly when you start car and gas fumes fill the inside of car. You can also feel the knocking

No to both questions

I first started smelling gas mostly when idle and of course my husband couldn't smell a thing. The third day I could hear a low knocking when I started the engin but not when I drove off. Day 4 loud knocking, strong gas fumes, and vibration from the knocking.

We found the problem. When changing the spark plugs, one of them was completely unattachted. That must have been the knocking noise. The gas smell was comming from a cracked hose leading to the plugs. We changed spark plugs and their wires and engin now purrs like a kitten.