difference between browseable and available directive ?

The "available" parameter determines is a client can connect to the share. If set to "no" then it is as if the share has not been created.

The "browseable" parameter determines whether or not the name of the share is included in the list of available resources (shares) when browsing the system. It is possible to connect to a share that has been set as "browseable = no" simply by using the UNC name.