I want to know which parameters needs to be modified in smb.conf to configure samba share so that it can be accessible from windows.
I want to configure directory so that some users get read only and for some users it should read and write both.
It depends what kind of security you want on your shares, as there's two different types of security over SMB, share-level and user-level. The difference between user-level and share-level is that share-level is purely based on passwords. Depending on your password, the system will decide what type of access to grant you. User-level security, on the other hand, grants individual users different permissions, and is thus more flexible.
Which one you choose really depends on your situation. If you've got a lot of shares and users, user-level security is usually easier, as keeping track of a lot of shares' passwords can quickly become cumbersome. However, if you have a relatively small LAN, setting up share-level security is simpler.
This explains it far better than I can, and detailed usage:
[Chapter 6] 6.3 Authentication Security