When sending XRP, you will usually need to provide a destination tag alongside a wallet address. These are two slightly different things, however, they are both essential to the funds ending up in the right place.
Think of an XRP wallet address as an apartment building, while the XRP destination tag is the apartment number.
Each Ripple wallet has an accompanying destination tag. This is a unique 9 digit code and will need to be given to the sender performing the transaction. When transferring XRP from your Oobit wallet you will need to provide a destination tag, as is the same with most exchanges. Some external XRP wallets may not ask for the destination tag.
To find your XRP destination tag, simply head to the dashboard and select the Portfolio option in the vertical left-hand menu. Scroll down to find the XRP wallet, and select Deposit on the right-hand side. The pop up will display your destination tag below the wallet address.