When your little one first learns to get into standing they often pull or push to stand. As their balance improves they are able to stand without holding on to support and become independent standers. Once they are independent standers they can learn to stand up from the middle of the floor! Sometimes they can learn this skill before they are proficient at standing, they just go straight into walking!
If you want to help your little improve in this transition, have various heights around the space they play in. Ideally they are all lower than their shoulders so they are pushing into standing rather than pulling into standing. When it is higher it is easier to bring their trunk and head upright once they are on their feet. They don’t have to move a large distance. The lower the support surface (like the floor), the more they have to move to get their body upright. If they are still working on grading their movements, they may overshoot or undershoot causing them to not stand up all the way. Don’t worry, they get better at this with lots of practice!
You can also give them a little support at their trunk or arm to give them just enough help to let go of the support. You may want to encourage them by having something up higher that they want to reach for.
Initially your little one may get into standing using a bear stance or a squat but as they improve their balance and get stronger and gain better control, they will get into standing using a half kneel. They may need to rely on using their hands initially but then they are able to do it without hands helping!