"Piled Higher and Deeper" by Jorge Cham
Below are some links with advice on preparing and delivering math presentations.
Technically Speaking: A project to improve the oral communication skills of undergraduate students in STEM
Blog post by Jordan Ellenberg: What to do in math talks
Blog post by Terence Tao: Talks are not the same as papers
Article in the Canadian Math Society Notes by John E. McCarthy: How to give a good colloquium
Your abstract should be a short description of what you plan to present. Keep in mind that this is a general interest seminar for people with a variety of different backgrounds and knowledge levels.