That saw looks excellent value. Pity they cheaped out by only providing one clamp although there are four receptacles for it in the base. Looks pretty much like the SIP one I got 14 years ago to build my workshop. They all seem to use the same design of base casting. But I got two clamps.
Frequently a bit more controllable to make cut by bringing the head down and sliding it rather than a vertical chop. I often use a combined movement to reduce the chance of lifting but thats not a novice technique as getting it wrong can make things worse.
Clamp the part to be cut firmly down into the corner between base and fence. Use a stop to set the length as there is no satisfactory way of marking the stuff. Measure twice cut once of course.
If you have a set of grip palm work gloves, either leather or PU faced cloth, you may be able to hold the main body down into the corner between fence and base. Use the heel of your hand. Not your thumb! Cut the longer spacers first. Free end will dance around quite wildly until you get it down to 500 mm or so. It will almost certainly try to escape as the cut goes through. Just had a quick play holding some offcuts down on mine. 40 mm Ø no problem, 25 mm Ø too small, no 30 mm Ø to try. Depends on your hand size and how well your gloves fit. I have small hands and use the stretchy PU faced cloth work gloves from LiDL. Cheap, comfy and made in my size.
Of course having done a couple or three sets got the knack and nailed down what it feels like when all is going well you'd dump the clamp(s) and do it free hand. Like wot Chris does and as I would. Albeit with a block of wood having a Vee out of one corner to help hold the material down.
Last thing. Chop / mitre saws are really, really noisy. I pretty much levitated first time I turned mine on!