Yeah I mean you need a tight, secure fist, with your wrist straight. It helps to wrap your fists.

Yes honestly I was just talking to someone about this the other day, "fight workout" routines without proper training are an easy way to get injured. I would at least take a couple beginner in person classes to learn the proper fundamentals

There are many ways to punch incorrectly. You can find this information anywhere, but here's a reasonably exhaustive account of how to safely throw a straight punch:

• Have a correctly formed fist, mainly meaning don't do something silly with your thumb (it should be under your palm but outside of your other fingers).

• Have a tight fist when punching, as others have noted.

• Have a straight wrist, as others have noted.

• Have a tight (strong) wrist when punching.

• Have correct leverage when punching. This is theoretically the most complicated part, but mainly what I mean for a straight punch is don't wing your elbow out to the side. The main power of a standing punch comes from your core and from the ground, not your arms (though strong arms will help, of course), so you need to align your body so that force goes from the ground to your knuckles, and the opposite force of the thing you're punching goes from your knuckles to the ground. If it gets caught up somewhere else, especially your shoulder (e.g. by winging your elbow), you will probably get hurt over time. This aspect is, imo, less intuitive for hooks, uppercuts, and overhands ("haymakers") but you can basically ignore it for something like a backfist. You should only be doing straights and I guess backfists if you like for a while and worry about other punches when you can throw straights well in combination.

• Make initial contact solely with the big knuckles of your index and middle finger, not your other knuckles or the rest of your fingers.

• It's cool to have wraps and/or gloves, especially for getting comfortable, but if it's a barrier to you (and wraps are pretty cheap, to be clear) then don't worry about it.

• Start by punching softly so that you can start developing a practical understanding of how to align your body. That said, always punch with "follow through," i.e. don't stop at the bag, strike as though you want your fist to go past the contact surface, because you do. This implies being slightly closer to the bag than where you could theoretically reach it from, by a few inches. It's also somewhat safer imo, because if you misjudge the distance and throw a punch that's to short, you still have a shallow punch, but if you are throwing shallow punches by default, then misjudging the distance might cause you to hyperextend your elbow. Meanwhile, for straight punches, if you misjudge the distance and jam the punch, that doesn't normally hurt because you didn't build up that much force in the first place.

• Make sure your body is aligned so that your torso isn't actively obstructing your rear arm, though you'll need to turn your torso regardless (even for your lead arm).

• Pivot on your feet a little. The foot under the hand that is punching (by which I mean left foot for left hand, right for right) should usually be turning on the ball of your foot (the part next to your toes) such that the heel wings out a little bit.

• The skin on your knuckles is probably very soft. If you aren't using gloves you might find that you need to stop not because you're tired but because you're wearing down your skin too much. That's fine and you'll develop callouses pretty quickly, and then it will stop being a limiting factor unless the bag is excessively rough or something (and then it'll just take longer to have callouses strong enough for it to not be an issue).

• If you feel pain in any joint, stop putting abnormal pressure on it until it is not in pain anymore, and consider figuring out why that joint was put in pain as the most urgent subject of your training.

• I suggest trying to read through this list a couple of times to have a notional familiarity with these points, then practice gently while focusing on a portion of them at a time, trying to incorporate more elements until you have all of them. I think you can get a basic handle on all of this in an hour or two if you don't get tired first, but it will take a lot longer to do these things by habit (though some things you can also practice outside of "practice," like just trying to internalize having your thumb in the right place when you make a fist by . . . making and holding a fist repeatedly).

• As others have noted, it is good to take classes. I'm just trying to cover most of the basic things needed for safety that you'd learn in a class, depending on the style. Having someone with experience observe your form and give you feedback is the best thing for helping you improve quickly.