How to access a samba share by a linux user?

That is only possible with shares that allow guest access.

Example smb.conf:

[global]
    map to guest = bad user
    # Use this instead of "bad user" with Samba 4.2 and later.
    #map to guest = bad password

    # Local user name for guest access.
    # Must have read permission on all guest shares and write permission
    #  on guest shares that should be writable.
    guest account = nobody

    # Other global options

[name_of_share]
    path = /path/to/share/
    read only = no
    guest ok = yes

    # Other share options

But note that this allows everybody that can connect to your server accessing the share(s) and you don't have user tracking (know who has accessed, created, or modified files).

To use password protected access (highly recommended), you have to create at least one Samba user with a corresponding Linux user, allow that user access to shares, and use it for connecting from Windows.