1. Use
1.1. talk about
1.1.1. things that happen regularly
1.1.2. scientific facts
1.1.3. instructions
2. Structure
2.1. Affirmative Sentences
2.1.1. Subject + verb + complement.
2.1.2. 3rd person: add "s" the verb.
2.2. Negative Sentences
2.2.1. 1st person
2.2.1.1. Sujeto + auxiliar (do) + not + verbo.
2.2.2. 3rd person
2.2.2.1. Sujeto + auxiliar (does) + not + verbo.
2.3. Interrogative Sentences
2.3.1. Yes/no questions
2.3.1.1. 1st person
2.3.1.1.1. Verb auxiliar (do) + subject + main verb?
2.3.1.2. 3rd person
2.3.1.2.1. Verb auxiliar (does) + subject + main verb?
2.3.2. information questions
2.3.2.1. Wh-words + Verb auxiliar (do) + subject + main verb?
3. Example
3.1. Affirmative
3.1.1. First person
3.1.1.1. I work in an office
3.1.2. Third person
3.1.2.1. I work in an office
3.2. Negative
3.2.1. 1st person
3.2.1.1. I don´t work in an office
3.2.2. 3rd person
3.2.2.1. He doesn´t work in an office
3.3. Interrogative
3.3.1. Yes/no questions
3.3.1.1. 1st person
3.3.1.1.1. Do I work in an office?
3.3.1.2. 3rd person
3.3.1.2.1. Does he work in an office?
3.3.2. information questions
3.3.2.1. What do I work in an office?