You can get to the upload page from two different places: the main navigation bar or the master left sidebar.
Click on the little cloud that says 'Upload'.
You'll be taken to the upload page, where you can click on the 'Select File' to choose which video you want to upload. You can also just drag and drop your files into the blue box to start the upload.
Once you select your video, you'll see a progress bar that'll tell you how much of your video has been uploaded.
In the meantime, you can start editing your video settings while you wait.
After the upload is finished, you'll be redirected to the settings page, where you can continue editing the look and feel of your video and publish any changes you've made.