What are pronouns*? They stand in place of a noun, e.g. they, it, I – and help you avoid repetition like: ‘Bob did this. Bob did that. Bob did the other.’
I’ll explain how to use them, and how to write about them in another post.
Below are the facts for reference. I teach them using various methods: coming soon…

First Person
I       me   my   mine (singular)
We   us    our   ours  (plural)

Second Person
you  you your  yours (singular)
you  you your  yours (plural)*

This grid looks odd, because most of the words don’t change. It does show how unclear English can be though. It’s not obvious when speaking to a group of people (you) or one person from the group (you). Usually, we say ‘you two’ or ‘you lot’. Other languages make the difference clearer. French, for instance, uses tu (sg.) for one person and vous (pl.) for more than one.

English used to have polite and informal versions of the second person. This lets you speak politely to someone important, or who you don’t know well by using ‘you’ (‘vous’ in French). For people you do know well, like your friends or family, use ‘thou’ (‘tu’ in French). This is used by Shakespeare:

Second Person (Shakespearean)
thou   thee   thy     thine   (singular informal)
you    you   your   yours  (singular formal)

Score extra marks in a Shakespeare essay by commenting on whether a character is using the formal or informal style. What does this tell us about the relationship? Is a character being rude by using the wrong tense: ‘you’ to show lack of intimacy, or ‘thee’ with a superior to be rude.

Third Person
he/she/it    him/her/it   his/hers/its  his/hers/its  (singular)
they            them          their            theirs          (plural)
Over half of all novels are written in ‘the third person’: he did this, he did that, or Bob did this, Bob did that.

Being familiar with pronouns helps with: studying languages, writing about literature (poetry, plays, novels, Shakespeare), KS2 SATs, KS3 English work and for the Reading Paper on the GCSE Language Exam.