First of all you need to have the Report file (.rdl). If you have created the SSRS Project by using BIDS/SSDT, you can click on Project and hit F4. Then you will see Full Path. Reports are saved in that folder.
You might be working as DBA and you need to get the Report file (.rdl) from version control software that can be Team Foundation Server or any other. You can simply check out the report file to your local folder. Once you have the report file. Then follow below steps
Open the Report Manager URL. It should be something like this
Once the Report Manager Interface is opened, you will see folders. If you have not created any folders yet, you can create folder by using Create Folder Tab.
To deploy the SSSR Report to Report Server, you need to click on Upload File and then browse to your Report (.rdl) as shown below.