Does double spending happen at all? I'm a complete beginner to anything and everything about crypto. I've been trying to research a lot about it, and I have recently just been trying to learn and understand some of the basics.
I was wondering if double spending ever happens at all?
Does it happen every day, rarely, or not at all?
It depends on what you mean by 'double spend'. Spending bitcoin just means using it to buy something. Therefore 'successfully' double spending bitcoin would just mean that you were able to buy something from two different people, even though one (or maybe both) end up being short of the bitcoin they thought they received.

The way bitcoin works is that there is a blockchain which contains all the bitcoin transactions that have ever happened. An interesting property of the blockchain is that the longer a transaction has been included in the blockchain, the more certain you can be that it'll remain there in the future. Transactions are added in 'blocks' which are produced on average every 10 minutes. 

In this way, merchants would decide how long to wait before considering a transaction as 'final', ie when they will complete their half of the exchange with a customer. So for example, if a merchant was selling a house, they may wait until 6 blocks before handing over the deeds. Similarly, a coffee shop might accept a bitcoin transaction even before it has been added to the blockchain, as long as they can see it has been broadcast.

Since most online stores would wait for say 3 blocks, and it probably isn't that profitable to pull it off in any coffee shops or bars accepting bitcoins, it probably doesn't happen that often. 

It's worth noting that nobody can know for sure how often double spends happen, not even miners. There's no information on the blockchain about whether bitcoins were successfully exchanged for other goods.