The registered user can able to log in from frontend as follows:
1 Click on the Sign-in button present at the top navigation bar

2. The customer would be redirected to the “Customer Login page”

The following fields need to be filled by the customer in order to sign up to his account:
1. Email/Phone: Enter either the registered mobile number or email id
2. Password: Enter the password already set by the customer
Once, the customer has filled the values, click on the “Sign In” button.
Once the customer clicks on the account page he would be redirected to My Account page, when “Redirect Customer to Account Dashboard after logging in” is enabled from the admin side.
To enable this setting, go to admin > Stores > Configuration > Customer > Customer Configuration > Login Option > set Redirect Customer to Account Dashboard after logging in to Yes.