, а то не могу понять как делать

Все предложения в англ. языке, кроме восклицаний, имеют сказуемое. To be используется во всех предложениях, где указано местонахождение предмета или лица.  Само по себе this не употребляется.  This is A day - предложение в котором есть и подлежащее и сказуемое, что правильно.  Is употребляется в ед. числе и are во множ.  Am употребляется с Я.

This is a teacher. / It is a teacher.
These are cats (these  как и галагол должен быть во множ. числе)
I am a pupil.
These dogs are nice.

This само по себе this/these может просто употребляться перед существительным и переводится как "этот" (these - эти).
  These pencils are nice.
I like this cat.

Но в значение " это (есть) ... " употребляются только this is/it is или these are (во множ. ч.)
These are books.
This is a book.

Finally, I went to university. Now I am a student. Many people think that student life is associated only with dormitories, with goolodom, despicable attitude. In some cases it is, but this time, positive emotions gorazdno more. During training at the high school, some students had continued difficulties and the negative side, but ask these students through a couple of decades of what was their student life, they reply that the most interesting and exciting. Why this is so is still unclear, but in addition to regular tests, seminars, exams and other things, there are good. For example, during training even high school, we all - still remain children who need to work during the pass and do not be late to class. And with good training students receive plenty of opportunities, for example, the opportunity to go abroad for the exchange and get a lot of unforgettable impressions and experiences. Appreciate while studying in higher educational university and wear the proud title of "student", because this is possible in your life will not happen again.