If you've never logged into FamilySearch before, create an account. That is done by going to: https://www.familysearch.org/en/, then clicking on the "CREATE ACCOUNT" box at the upper right corner of the page.

If you would like more instructions, click on the question mark in a circle just to the left of the "CREATE ACCOUNT" box. The help box shown here at the left will pop up. Then click the link that says, "How do I create a free FamilySearch account?' That should tell everything you would need to know.