I'm new to SketchUp

Try this:

Pay attention to the scale of things. SU was designed for architects in the first place, so SU regards points close together than one thousandth of an inch as meant to be the SAME point. And it doesn’t like small edges for much the same reason.

So if you are modelling things with small details, (in mm say) it’s best to draw with metres representing mm, then scale down when you are done. SU won’t create small edges (created, for example by the FollowMe tool), but will preserve them if scaled down from a larger size.

SU circles and arcs are drawn with short straight edges, though ‘meta information’ is stored specifying ‘real’ radius when you draw a circle or an arc. That meta-information is lost if you join an edge to the circle or arc other than at the end of an arc.

A common error is to use too many segments in arcs and circles for the scale of what you are drawing. For example, I’ve drawn structures using scaffolding with pipes and clamps using only 8 segment circles, and they look absolutely fine (and round! ) except in really close up views. That starts to matter if you create large models.

See my earlier thread on simplifying 3dwarehouse models for use as architectural entourage (supplementary details to a modelled building) at https://forums.sketchup.com/t/simplifying-3dwarehouse-models-for-use-as-entourage.

Learn to draw cleanly. If you don’t get it right first time, it’s usually easier to draw it again from scratch than to fix it with extra lines.

That’s a digest of some of the things I’ve found out the hard way using SU over more than a decade, and covers most (or at least many!) of the errors I see on this forum new users commonly make by ignoring these things.

Best wishes for your future modelling.