There are four sentences in a general introduction paragraph. They include:
Hook: This grabs the reader's attention, and is relevant to the topic
Topic Sentence: This goes into some detail of what you are writing about, but does not give away any information
Thesis/Main Idea: This is the most important sentence of the ENTIRE essay. It specifically shows what you'll be writing about, and what you're trying to prove. It is your argument.
MAP: Your reasoning behind your argument. These are the specific points that will help prove your main idea. They are also the way you'll be dividing your paragraph.
Here is an example introduction for an argument saying that Lionel Messi is a better soccer player than Cristiano Ronaldo:
(Hook) Someone is always striving to be called the best in sports. (Topic Sentence) There have been many great rivalries and comparisons between players as to who is undoubtedly the greatest player/team. (Main Idea) The easiest argument out of these to make is that Lionel Messi is a better soccer player than Cristiano Ronaldo. (MAP) Messi is clearly a better player, and shows this through scoring goals, creating scoring chances for others, and winning more championships.
*My next 3 paragraphs will be divided into my specific MAP points.*
Need Help? here is a video that puts the writing process into another point of view: