We often have many different things to do. This can become very exhaustive, because we think we need to do everything at once.
But we don't have to do it. You just have to pick one thing with the highest priority and say: "I will work on this task for 2 hours now." or "I will do this one thing until I reached X."
And you can then just write down the other tasks with lower priorities. You can't do everything at once. It is impossible. Even multi-tasking is a myth. Just make sure you work on the thing with the highest priority. Even if it feels like you wouldn't make any progress, or only little progress, there is nothing that could be time better spent than on your highest priority.
And after some hours or days working on your task with the highest priority, you can pick again the task with the highest priority. Maybe it is the same task, or it is a different one.
And you don't even have to sort the other tasks based on priority as well. Just picking the task with the highest priority is runtime complexity O(n), while sorting each task based on your current priority is O(n log n). But after you finished working on your top priority task, you might feel like your priority changed, you have to scan the tasks again anyways (O(n)), and can't just pick the task with the highest priority. So you can just leave the other tasks unordered.
But this emphasizes the importance of having a calender or list to write all tasks at hand down.