Duration is the span of time (in working time defined in the calendar) from the start of the task to the finish of the task. Work is the amount of effort expended during that time.

For example: You may ask a resource (Jane) to help out on a task. You ask her "when you will have it complete?" Jane tells you she'll have it done on Friday. Assuming today is Monday the duration of the task is 5 days. However, Jane is assigned to three different projects and she know that it really is only 12 hours of work. She has increased the duration to longer than 1.5 days knowing that she is going to try to fit your task in among the other work she's doing.

Another example: You have a 2 hour meeting scheduled. You've invited 10 people to attend the meeting. The duration of the meeting is only 2 hours but collectively there will be 22 hours (10 invited plus you) of work expended during the 2 hour meeting.

Duration drives dates (start and finish). Work drives cost and resource availability.

Regarding your question around your project where you are the only resource. Chances are your boss is going to be interested in duration (dates). It will be up to you to estimate your relative availability to the project. Assuming the project is not your 100% full time job, the difference between work (effort) and duration is a factor of your other, non-project work.

As you are the only resource, you are likely going to want to link your tasks Finish to Start. I would use Auto Scheduled tasks and let Project do the heavy lifting for you.