Although there are a number of things you can do at FamilySearch.org without signing in, there is a lot more you can do if you sign in with a free account. (You can use your LDS Account username and password.)
Without signing in, you can still search the catalog, digitized books, genealogies, the Wiki, and the learning center. You can also view user-contributed photos and stories. But if you sign in, you will be able to access historical records and the Family Tree. You will also receive personalized help and notifications.
A FamilySearch account is, and always will be, free. FamilySearch never shares your personal account information with any third party without your consent. Learn more about creating a free account on FamilySearch.org.
Learn more about the personalized experiences on FamilySearch in the article “Enhance Your FamilySearch.org Experience with Free Sign-In.”