Just for clarification:
There are TWO systems in use.
In most independent establishments Wi-Fi is accessed in exactly the same way as it is in your own home. i.e. you search for the signal, and make your connection, via the Wi-Fi icon at the bottom right of your screen. You'll then be asked for a password, which is likely to be displayed on a wall or on a menu card; otherwise you'll have to ask the staff for it. (A small number of establishments don't bother with password-protecting access to the Wi-Fi, so you might not need a password at all).
In most 'chain' establishments, such as Wetherspoon's pubs, Tesco, McDonald's etc, you also connect in the same way but, in the first instance, you'll find that no password is asked for. However when you try to access a web page you'll then find that your browser is diverted to the login page used by the relevant establishment. That will probably only ask you for your email address before allowing you to carry on browsing but a few places have rather more complex systems. Asda, for example, asks you for your mobile phone number and sends an access code to that number, which you then have to enter on the login page.