Beetles & Bugs
When Starting out with beetles, it can take a little while to differentiate them from other insect orders.
The most commonly confused order is that of the True bugs, Hemiptera. In the field, I often still get caught out by some of the incredibly convincing ground bugs until closer inspection.
But there are some fairly simple ways to split them by eye fairly quickly.
I am no expert in Hemipterans, but British bugs has an exceptional library of reference images that should solve most, if not all, of your true bug-related queries.
True bugs always have filiform (threadlike) antennae (although they may be flattened) and have less than 10 segments (usually 5-7) which are much longer than wide.
Beetles can have all kinds of antennal segments and if they are filiform they will usually have between 10 and 12 shorter segments.
Beetles have chewing mouthparts consisting of two jaws and 2 pairs of palps
(one pair usually being fairly obvious)
True bugs have a tube to feed with, no jaws or palps. Usually, the feeding tube (rostrum) is tucked along the underside of the body.
In beetles the wing cases always meet in the middle along a central line forming a 'T' Shape
In true bugs the wing cases meet to form an 'X' or 'Y' shape.
If your specimen instead has 'wing buds' it will be an immature true bug as immature beetles look very different from their adult forms.