After this I further want to understand how create models such as one shown below - as you have done in your home page.
Well, this specific model is exported from some advanced CAD package, likely NX. It is hypothetically possible to design something like this with OpenCascade, but you can see lots of smooth blends and spliny transitions over that model. The latter is definitely not the strongest side of OpenCascade.
Please suggest me the steps - I would be very thankful to you.
Given your background, I think you're not going to have much troubles with the library. The typical learning path consists of passing a training on OpenCascade. That's something the OCC company sells for money and something we try to do on youtube for free (not sure if this content is clear and concise enough though). Methodologically speaking, trainees pass the following steps:
1. Learn OpenCascade basics, such as memory management, utilities, etc.
2. Study geometry, the mathematical form for curves and surfaces, parameterization, tools to construct geometric primitives.
3. Connect geometry with topology, getting to B-rep principle of modeling.
4. Learning modeling API.
5. Higher-level services, such as OCAF, visualization, data exchange, shape healing.
Speaking of practice, the following steps are typical:
1. Create a sketch (without a constraint solver as there's no solver in the lib) as a train of trimmed curves converted to edges and wires.
2. Extrude a prism and this way switch from 2D to 3D.
3. Run different modeling API on the prism, e.g., Booleans, fillets, etc.
4. Export the modeling result to STEP.
The items above compose a typical agenda for a workshop if you do not have any specific needs for what exactly you're trying to create. For people developing some CAD application, the learning path is usually full of trials and errors.
What you definitely can do is keep hanging out with us on the forum and ask random questions whenever you come across some modeling or programming issue.