According to NASA it’s a regular repeating path that one object in space takes around another. Now as for getting into orbit, it’s quite easy.
An orbit has an elliptical shape, usually with a farthest and a closest point. These points are called apsis, the periapsis is the closest point to the body, the apoapsis is the furthest point to the body. This is how an orbit can be identified. To get a higher periapsis you have to burn prograde at your apoapsis, and to get a higher apoapsis you have to burn prograde at your periapsis. Prograde means the direction you’re moving in, or in this case orbiting. Burning retrograde you can get a lower apoapsis or periapsis.
One thing to note is that if you burn too much at one point it could cause them to swap, why? Since you might have completely turned your trajectory upside down.
How to get into orbit?
You get into orbit by starting to fly at a very low prograde angle, if this is not possible(the game or rocket you’re using doesn’t have the systems available) you’re going to have to guess the angle. Once you leave the atmosphere you want to keep going as sideaways as possible until your rocket has orbital velocity, this depends on altitude and gravity.
Once you have enough velocity, you can then get to your apoapsis by waiting. Your apoapsis will be available before your periapsis since your initial trajectory will be parabolic this is because you aren’t in orbit yet and will have a normal flight like a very highly fired bullet. Once you get to your apoapsis by waiting, you can then burn prograde(hopefully you can get that automatically calculated otherwise you’re going to be in mild pain randomly burning until you find it). You then basically raise your periapsis until it’s above the planet’s atmospheric zone, or as high as possible, there will always be tiny atmospheric particles that leak from the planet to slow you down. You try to minimize drag as much as possible.
Getting into orbit quick tips:
Gravity turn/prograde turn from launch
Leaving atmosphere go sideways as much as you can to get into orbital speeds.
Once in orbital speeds stop and wait for apoapsis(you want it high enough so you’re not in the atmospheric zone)
In apoapsis burn prograde to get your periapsis up to above the atmospheric zone.
Optional: Go to your periapsis and burn retrograde to make your orbit more circular.