Cutting your own firewood is a very satisfying thing to undertake. Not only will you save money, but as Henry Ford said, you’ll warm yourself up twice. You’ll need to make sure you have the right tools in order to cut wood up into firewood. I’d recommend going for a wood splitting maul. They are heavier, with a wider head so you can cut big pieces of wood with ease. Axes will work, but it’s much harder with them unless you really know what you’re doing.
Don’t try to cut wood that is an unusual shape or has nails in it. It’s a safety hazard and really not a smart thing to do. The nails can damage the axe/maul, or worse pop out and go into your eye. Don’t risk it. Also, don’t cut your firewood near anyone else or something that can be damaged. When you strike the wood it can pop out and hit something nearby.
You want to be splitting the wood across the grain/lines. If the wood has any knots in it then I recommend not trying to cut it as it’s just not going to work. First, place the wood down on a level surface and stand at arms length. Swing up and down hard, aiming for the lines. It’s not that hard to split wood. It doesn’t require massive force, just accuracy and hitting it at the right spots.
If the wood doesn’t split straight away, just keep going at it trying to hit it near the same spot. You want to get enough driving force to smoothly split the wood and not get your ax or maul stuck in the wood, which is really annoying because you’ll have to try to wrestle it out and if the wood is small/light, then that can be quite challenging.