how to create a new sketch for new part based on reference sketch into another part?
TLDR: Use 'insert > part' feature to insert solid geometry, planes, sketches, axes, surfaces etc., depending on your needs, of one part (part A in your case) into another part (part B) which enables you to reference part A within part B. When part A is modified, those changes in turn will drive the geometry in part B.
This is a great question!
What you are referring to, and wish to accomplish, is often referred to "top down design", and is something not enough designers that I've been involved with along the way do. Most just model part A, then model part B, then assemble them, and go back and forth between them "tweaking" dimensions until things line up correctly. This is an incredible waste of time, and gets worse the more parts there are.
A robust "top down" system design starts with a "base part, or master part" as some call it. The intent of the master part is to capture critical design information such as system envelope, part-to-part interfaces (hole locations etc) and anything else that affects or relates to multiple parts.
This "master part" is then inserted (usually as the first feature) in all the downstream parts, and the 'real' parts are developed from and around that.
My master parts typically have several solids (multi-body part), surfaces, and sketches, and get re-visited and added to often as the detailed design progresses.
The advantages of designing a system this way quickly become apparent as adjustments to the master part are made and the entire system design responds to the updates. You can make massive updates across many parts with a single change to the master part. Also, assembling the downstream parts requires no mating (unless you want to) as parts are modeled from the start in their correct locations relative to one another, and drop right into the assembly in their correct location in space by default.
Also, using a master part eliminates the "circular references" problem when trying to relate parts to each other with "in-context assembly references", which is the other way to relate one part to another, but trust me, never ever do this. Use a master part.
Good luck, and rest easy knowing you'll be light years ahead of almost everyone else if you stick with "top down" system design methods.
There is a 'delete body' feature you can use on any extra geometry at the end of the design, leaving you with just the one part.
thanks for this great explanation. But then what do I do with the insert part, once part B is done? I hide it? Can I keep relation between sketches of part A and part B or the relation exist only between geometry and not between sketches?
Couldn't have explained it better