That’s quite easy, just install the Samba Server from the MyOSMC - AppStore. Then the OSMC box becomes a Samba Server and can be accessed from Windows. While this will only give you restricted access to the OS files you should use SFTP to access those if needed.
From my experience the most stable and flexible way for that is using autofs using SMB following this guide
Well you may can ignore learning most of them and just follow the HowTo’s but it might not be bad to google some of them:
SMB (Server Message Block) is a networking protocol mainly used natively by Microsoft for network file sharing. Samba is a free implementation using SMB to act as a server (e.g. on linux).
FSTAB (File Systems Table) is a fundamental part of Linux that tells the operating system which filesystems (Harddisk or Network) to mount (where and how). For long the fstab was a central part for this. In modern times where filesystems became more “flexible” (USB sticks, Network FS,…) there are also alternatives to the fstab like the autofs solution we explained above.