Your clients do not need an account or login.
Nevertheless, there are two different, easy ways to send galleries to your clients.
Directly
Send your clients the direct URL to your gallery - they don't need to log in unless you have set a gallery password in the gallery settings. This is the fastest, most convenient and most used way.
You can send the address to them by e-mail, messenger, etc. Or conveniently via picdrop by clicking on "Share" in your gallery.
Via client login
You can create clients logins in your account settings. You can set a login and assign it to one or more galleries to which your client will have access. Afterward, you point your client to your picdrop URL (https://www.picdrop.com/your-username). There he/she will find a login field in which he/she only has to enter his/her password. After the successful login, your client will see an overview of all the galleries that have been activated for him/her. It is important to understand that the client login has nothing to do with the password of a single gallery.
Furthermore, it is important to know that noone is able to see your gallery overview. This overview is reserved for you, as the account owner only. Therefore, it makes no sense to refer clients to your own picdrop URL unless you have created a client login for them.