Present simple. This tense is used to describe an action, habit or facts that are generally true and occur in the present time. The structure is subject plus the verb in the present form. For example, I walk to work every morning.
Anna visits the town centre every weekend. She works as a teaching assistant in the school. If you're using I, you, we or they, the verb doesn't end with an S. However, if you use the subjects she, he or it, we generally add an S to the verb. For example, walks, visits, works, goes.
Present perfect. This tense is used to describe an action that has taken place once or many times before now. The structure is subject plus have or has plus a verb past participle. For example, I have walked to school every day.
They have traveled to China twice. Stacy has worked as a teaching assistant for three years now. It's important to remember the time period is still continuing. For example, Stacy's career is still continuing. Therefore, we use the present perfect tense.
It's important to note for subjects I, we, you, they, we use have. For subjects she, he, it, we use has. Present continuous. This tense is used to describe an action that is ongoing now.
The structure is subject plus am, is, are plus a verb ending in ing. For example, it is snowing outside. I am studying for my exam. She is eating her lunch. For subject I we use am, for subject she, he, it we use is, for subject we, you, they we use are. Present perfect continuous.
This tense is used to describe an experience or an action that started in the past and is still continuing till the present moment. The structure is subject plus have or has been plus a verb ending in ing. For example, I have been studying for three hours now. They have been living in the same house since 1999. It has been snowing all morning. For subjects I, we, you, they, we use have. For subjects she, he, it, we use has.