If my budget is £500 for a Gaming PC - what would you advise me to do ?

If your poor (like me) you're probably best off getting a second hand case, and going with something on par with a gtx 1650 super. If you can try buying second hand but be careful, especially if they don't take refunds.

you cant video game with only 500. only 600 can geam

Depends on the games you want to play and your current PC.  For that price if you can get something that upgrades the GPU and memory but you can reuse your current gpu while you save for better it may be worthwhile.

Are you upgrading or starting new? What do you have just now? what games will you be playing? 

Gaming PCs cost more than that because people use video cards to mine Ethereum, driving up the cost of the equipment. A good new one starts around £1000. Buying a used gaming PC is risky because you can end up something worthless and unable to return it.

For under £1000, it isn't a gaming PC.

To stop gaming and get a life.