can anybody help me here to figure out how are these designs made? Like what software and what tools can be used to make similar designs?
Nearly anything goes, but a vector drawing program is the easiest. I mean such as Illustrator, Inkscape, Affinity Designer, CorelDraw or Xara Designer. They have smoothed pencils and the pen for Bezier curves. Preset curve drawing tools make regular outlines such as ellipses, rectangles and circles easily. Drawing is possible even with a mouse.
Mouse is often very inaccurate. If you get exactly what the mouse outputs, you can get for ex. these:
Using smoothed pencil tool with a mouse gives easily these:
Of course you can in a vector program apply smoothing and make edits afterwards. Very trivial edits convert the results to these:
If you have a graphic tablet (Wacom etc...) you can get perfect looking curves with minimal edits in the first day you have it. When compared to a mouse a good graphic tablet lifts your drawing productivity hundreds of percents.
Illustrator maybe is a step ahead the rivals because it has perfectly working tools to fill areas which are limited by open curves and lines. Its Shape Builder is still the best. Think for ex the black wide stripes of the bee. They can be colored in a few seconds in Illustrator, no matter their borders were separate items, not carefully assembled closed paths like some other programs demand. Inkscape is free and it also has area filling tool (=the paint bucket) but it's very inaccurate. Affinity Designer hasn't even it.
Here is drawn some a little resembling shapes for the bee. This is in Inkscape:
The main body shape is a little crunched ellipse, the cheeks are circles, everything else has been drawn with the pen. The smoothed pencil would be handy for those numerous black lines in the wings, in the body, the feet and the antennas.
Your bee clearly has duplicated parts, for ex. the wings. The fish has plenty of them as a tiled pattern. Vector drawing programs have tools for making copies and tilings.
Vector drawing programs have steep learning curves. A beginner should get the documentation and patiently work the examples and available tutorials to get started. Trial and error is here extremely wasteful learning method.