The above list is not exhaustive, but it's a great starting point. Washing machine repair is by no means a simple task, but it becomes a lot more manageable for the average homeowner when you're at least somewhat familiar with the parts that you're looking at. Take a minute to look over the owner's manual that you received when you purchased your current unit; there should be a complete diagram with all of the parts labeled. If you misplaced the manual or can't locate a helpful diagram, there are countless online resources that can help you with your DIY repair by allowing you to look up your exact model specifications and helping you identify exactly which parts may be at the root of your washer's malfunction.
You might be wondering if it is really worthwhile buying online as there is the freight to consider. But don't forget that your bricks and mortar stores also have to pay freight on the parts they get - and they then pass that cost on to you, as well as their other overheads. By buying parts online you can often get steep discounts as online stores do not have to pay staff or rent for a shop front. And often they will give you free freight if the cost of your purchase is over a certain amount.