These words tell us who is who in a sentence. Your grammar textbook will call these “Personal Pronouns” or “pronombres personales”, but you won’t need to know that term in order to use them. Try to memorize these words. For some people, me telling them to memorize these words is all it takes. For others, it's not that easy. If you are unable to memorize them right away, don’t be discouraged. They will be repeated almost every time you interact in Spanish. Eventually they will stick.
yo - I
tú - you (informal)
usted - you (formal)
él - he
ella - she
nosotros - we
nosotras - we (all female group)
ellos - they
ellas - they (all female group)
ustedes - you guys, you all, y’all
(vosotros)* - you guys, you all, y’all (Spain)
(vosotras) - you guys, you all, y’all (Spain)
You will soon learn that "yo", "tú", etc. are often optional to use in a given phrase. For now, it's okay to keep putting them in every sentence. Use them exactly like you would in English. Over time you will naturally start to drop them out of sentences like a native speaker will often do.
*In this study guide you will see an intentional focus on Latin American Spanish. Since "vosotros" is a term that is primarily used in Spain, the majority of Spanish speakers on the planet do not use this form in their everyday lives. It is more than possible to get by speaking Spanish without ever having used it (I never use this form unless I'm teaching it or want to poke fun at my friends from Spain, jajaja).
If you do go to Spain, you will hear "vosotros". A high percentage of Spanish 101 courses include it for this reason, and so we will cover it in this study guide. However, considering the fact that there are more Spanish speakers in Los Angeles, California than in Madrid, Spain, the "vosotros" form might be one you choose to focus less on, if at all.