To import features from a CSV file, first you need to prepare such a file.
Go to the "Import" section by pressing the according button in the main menu.
On the "Import Features (CSV)" tab you will see the "Instructions" section where you can read about what are the requirements for the file that will be imported.
On the same page press the "Select File" button and choose a file from your file system.
Then press the "Upload" button and the file you've chosen will be uploaded to the server. After this, you will see a table with headers from your file so you can verify that it corresponds to the first row.
Now you have to manually map each available feature field to a header in your file so data can be set correctly during the import process.
Press the "Start Import" button to start the import
You will be able to see the import process status at the top of the page. After the import process finishes, there will be the latest import stats displayed.