I've tried to organize my to-dos using various digital solutions and while they certainly had a lot of features, they all fell short of motivating me to complete tasks.
So I've since switched to a much more simple system. All it requires is a pencil and a stack of sticky notes. You then write your to-dos on one sticky note each and put them on a stack.
It is important to not write down too many to-dos at once, as this will just lead to you overwhelming yourself. Instead, keep it limited to a small number (something like 5 notes).
Whenever you work on a certain task you just put that sticky note on your desk, monitor, or wherever else. What matters here is that you see the note regularly throughout the day. This constant reminder is part of why this approach works for me.
When you've completed your tasks you move the note onto the pile of completed tasks. I know this sounds simple, but it is the physical feedback of that action which triggers a sense of accomplishment. Seeing the pile of uncompleted tasks shrinks while the pile of finished tasks grows is motivating. You can literally start applying this within minutes because it is such a simple method.