Firstly please understand that I am not a Tutor.
I do understand where you are coming from with regard to experience and Software familiarity.
The demise of the free downloadable version of SketchUp forced me to consider less expensive alternative options.
This Forum has many Members prepared to help, especially if the less experienced S3D User is willing to help themselves. This help is free with no strings attached, why not try asking a question and go forward from there? Your ongoing choice(s) will be respected.
When considering investing in New Software it is prudent to ascertain what it is capable of doing, in your hands. It is pointless wishing that it could do, what you want it to do, in the manner it could be done in familiar software.
My MO learning about S3D was to choose a Menu, in perceived order of priority [e.g., the Main menu on the side], and then open the first/top Tool/Feature Icon.
Whatever was revealed by clicking an Icon was investigated to see how it functioned, what I could achieve by using it or how the the information presented would help my understanding.
IMO there is no substitute to gain knowledge and familiarity, efficiently, other than actual use.
There is need to ensure that every Tool/Feature is investigated, say by checklist, but you do not have to do it in strict order. Quite the reverse, as you find things that are useful make prompt use of them and it can be surprising how quickly things fall into place.
At this point you will be thinking about the time this will involve, but at some point you must assimilate sufficient information, by your own efforts or from a Tutor.
Assuming you will ask a question, bear with me for guessing that it would be about Modelling Tubes [given that these could be used to construct the BackPack Frame mentioned above].
The following give some pointers to how this could be achieved.
Forming a Frame using Sweep, during the Sketch some of the Points were locked previously to keep within the video size limits:
So a Frame requires serious changes, Hide the old Body, modify the Sketch, and of course to finish you would ned to Sweep it again:
A further change to the Frame Shape, this shows the origin of the Curve used for the Change:
A little more Sweeping and then a Mirror:
S3D is capable of almost anything you throw at it.
Notice the cost, only a short time, noting that when I tried to upload this around 08:30 GMT I have had to wait 8 or so hours due to the Forum being [extremely unusually] Down.
Feel free to Message me if you consider that best for you to impart the problems you have.
I will do my best to respond promptly.
Hey, if it does not work for you there will be nothing lost?
What is in it for me, keeping the Grey matter active and helping to build a strong Community, the latter protects the Investment by helping to maintain S3D’s Customer Base.