Adding stocks/ETFs to basket is super easy! Check out this article on how to initiate placing an order.
Once you click on Place Order using any of the methods described above, you'll see a dialog like below:
You can select the order type - Buy/Sell and specify the quantity. Clicking on Add to Basket will then add the stock to your basket.
If you click on Buy (or Sell) Now, the stock will not be added to your basket and you'll be taken to the confirm order flow with only that stock. Don't worry, your basket will not be affected!
Alternatively, you can also copy your watchlist to your basket by clicking on the Add all to Basket button: