First, welcome to TCDB. Ask (as you did here) and someone from the membership will gladly help.
Atop the right-hand side (assuming you're on a PC/Laptop and not a phone) and where you see your ID there's a drop-down menu, and just click on Collections. It'll take you to the Main Collection page where once you begin logging your collection, wants, trade/sale, etc. will be shown. There's a green button to "Add/Update Cards" and click on that and you should be on your way. Just keep clicking and you'll figure it out. If you need more help, let us know.
Follow my blog - I Identify as a Card Collector.
“Aslan didn't tell Pole what would happen. He only told her what to do. That fellow will be the death of us once he's up, I shouldn't wonder. But that doesn't let us off following the signs.” - Puddleglum in The Silver Chair by C. S. Lewis