I made the upper part of Glock 17 but i do not know what is right way of retopology ?
the retopology i did is right or not ?
The model without retopology :
g17.blend (993.7 KB)
Retopology by me :
g17-2(after dissolveing more ).blend (954.1 KB)
And also i wanna know how to do hard surface modeling ?_?
Now you have a lot of n-gons.. this might be tricky. You can do somethign like this:
Triangles at planar planes are not that problematic..
Also your part is still only paperthin.. you should solidify this before optimizing because the way you want to retopo this depends on the final form.
There are multiple singular tips about hardsurface modeling problems and of course complete courses. So that’s not a question to answer easily. It also dpends on your current skill level and the way you “like to be teached”.
The description of Topology’s method is not easy to explain briefly because it is extensive. And it is a modeling method that applies a lot of individual personality.
A request for help with an unresolved problem during an attempt will be more helpful. 
The link below is a YouTube channel that covers Hard Surface Topology.
If you don’t need a lecture on how to use a blender, look at how to handle Hard Surface Topology in different software.
Just to give an example.. this may be fine.. explicitly using the shiny matcap..
but i screwed up a little on some border vertices.. 
oki-g17.blend (133.3 KB)
