Learn the support swing on parallel bars: rail width, arm position, build-up to forward and backward swing, typical mistakes like hollow back and bent arms.
In the support swing you support yourself with straight arms between two rails and swing your straight body alternately forward-up and backward-up — buttocks and toes at least at rail height [2]. It is the base of almost all parallel bars elements: the Swiss teaching material writes that swinging and the swing-up to support form the basis of parallel bars work [3].
The honest answer to "How hard is it?": It looks like little but is work for the shoulders. You have to carry your body in support and swing at the same time. The German accident-insurance material names collapsing arms with insufficient support strength as a typical cause of accidents on the parallel bars [2]. In other words: strength counts more than courage.
A correction of expectation: in competition mere swinging does not count. Back swings in support that do not lead to a value part but merely reverse direction are deducted there [4]. For you, swinging is not a competition part but the tool.
Support on the rails, arms turned slightly outward, the crook of the elbow pointing forward [1]. Push the shoulders out [2]. Milestone: ten seconds of support with straight arms without sinking in.
Jump from a box top into support and swing forward to the straddle sit [1]. Alternatively you go in support from box to box through the rail lane [2]. Milestone: five jumps into support, arms stay straight.
Start with a small amplitude. The material recommends exactly that because spotting is then better [3]. Two elastic ropes at the front and back that you touch with the thighs serve as a marker [1]. Milestone: ten pendulum swings between the ropes without the arms buckling.
On the forward swing you take a slight C+ pose (navel to spine), on the backward swing you are stretched in the I pose or a slight C− pose [1]. The angle between arm and trunk opens in the swing and closes only when passing through the vertical [2]. Milestone: buttocks and toes reach at least rail height [2].
On the forward swing your gaze goes to the end of the bars, on the backward swing the head stays in line with the trunk [2]. To finish you can swing in support through the whole rail lane. Milestone: ten swings in a row, clean shapes, checked with a side-on video.
Hang two carpet tiles with bells in the rail lane and try to hit them with stretched feet. The method appears in the German school material and gives you instant feedback on whether you are really swinging stretched [2]. The distance between the tiles must not be too big at first [2].
Rule of thumb: rail distance equals forearm length, from elbow to fingertip [1][2]. That way you can turn the crook of the elbow forward and support stably.
Buttocks and toes at least at rail height [2]. More important than height is shape: straight hip, straight arms, shoulders active [2].
Usually it is support strength, or the crook of the elbow does not point forward, or the shoulders sit too far in front of or behind the hands [1][2]. Practise the support on the floor and with a helper who lifts your legs [1].
At the beginning yes: with a clamp grip on the upper arm and one hand on back or belly [2]. The aim is that spotting quickly turns into a light safeguard [3].
That is a question of experience. Many swing calmly after a few sessions. How many exactly depends on your support strength. There is no fixed study figure for this.
Learning the Front Hip Circle: The Belly Wave on the Bar Where the Legs Have to Keep Rotating