Hello,
I'll explain them step by step to make it easier.
To change your default browser: First, open Google Chrome. In a new tab, copy about://settings/?search=default+browser into the URL bar at the top (where you enter web addresses). Click enter, and then once it loads, you should see a button that reads on the screen, "Make default".
Press it, and then it should open the Settings app. Let the list of apps load, and then it should take you directly to a screen that says, "Make Google Chrome your default browser", along with a list of file types. Select "Set default". Google Chrome should now be set as your default browser.
To sign into your Google Account, go to https://google.com/ and then once Google loads, select sign in at the top right. Enter your email address and then enter your password. If you are asked to scan a QR code to finish sign in, open the Camera app on your phone, and then hold your phone over the QR code (make sure it fits in the frame). You should see a popup to a link somewhere on the screen; select it, and then complete the steps to sign in. The phone may ask for your password or PIN (the lock screen method on the phone) to be able to complete sign in.
Once you are done with the phone verification, on the computer, check if you are signed in.
Please let me know if you need any part of this clarified, I would be glad to do so!