When you say “recover” your ost, what do you mean exactly? The ost file is the file created when you set your outlook client to cached mode. It is the local cached copy on your pc. If it becomes corrupted all you have to do is close outlook, delete the ost and then re-open outlook. It will rebuild the ost from scratch. The time it takes depends on the size of your mailbox. There is no need to back up the ost, it is just the local cached copy of the exchange mailbox. If the exchange mail store is being backed up then you do not have to back up your ost.
For OWA, start with this article, then follow the link to configure the SSL certificate.
If you are asking how to recover a lost mailbox on the server from the ost on the client, there is software you can use for that. Do a search for “recover mailbox from ost” and you will see many different software products which will allow you to restore from an ost.