Also what are these multiple addresses stated under addresses tab; Why have so many receiving addresses, have to manage the private key for each.
All these addresses are yours and are created from your seed phrase and can be recreated from it in the future (eg. recovering the same wallet using seed phrase), in other words seed phrase is the only thing you need to write down as backup.
You can choose any of them to use, there are multiple and each time you use one a new address will be created to encourage avoiding address reuse.
difference between receiving and change address?
Technically there is no difference, they are all bitcoin addresses and are all created from the same seed phrase. But practically the wallet categorizes them differently so that it can send your change to a different group of addresses to somewhat increase privacy.
wasn't able to find my wallet address under the receiving tab
Not sure why it doesn't show up in this tab, but this tab is a simplification of the Addresses tab where it selects the top unused address and shows it here for you to use. When that address is used, next time it shows the next unused address; all of which can be found in Addresses tab.