Yes, there is a difference between pre-qualification and pre-approval.
Pre-qualification is a less formal process involving no credit checks. It's based entirely on the documentation you submit. You can get a pre-qualification done online or over the phone. Since it's based on your documentation and not on official checks done by the lender, it's a rough estimate of what amount you'll be pre-approved for.
A pre-qualification will give you a very rough picture of what budget you'll have at your disposal for your next home purchase. Or at least a good-enough estimate so you can start browsing homes online. It indicates what you can afford, so you don't set high expectations.
! Do not submit any offers if you're only pre-qualified. You should start submitting offers only after you've been pre-approved. Most sellers will not take your offer seriously without pre-approval, and you might lose a home you really liked.
You can start the pre-approval process at your bank. However, it's ok to shop around and see if any other lender can offer you better terms. A mortgage broker can help you find the best possible option.
If you want to expedite your pre-approval process, you can ask your preferred real estate agent to help you. Most agents, like myself, have established contact networks with a few mortgage brokers and have our contacts within individual banks.
Remember, even getting pre-approved DOES NOT guarantee you can take out the stated amount. Also, if interest rates change between pre-approval and purchase, you must repeat the process. In this case, your lender will likely adjust your pre-approved amount.
It's not wise to start looking at homes without getting pre-approved. You risk falling in love with homes that could be out of your reach. It will then become challenging to find a property you'll love after seeing all those fantastic homes that are out of your budget.