This question is too broad to answer thoroughly in the space allotted. "The" is a definite article. "A" is an indefinite article. Articles are a pretty basic grammatical feature in English - many resources exist to explain this concept, e.g. https://owl.english.purdue.edu/owl/resource/540/01/ I know Russian doesn't have articles so this can be a real challenge for Russian speakers. The other words are all prepositions. They are some of the most common English prepositions and each of them can be used in many different ways. Daniel, above, has given you one example for each, but there are many other different ways to use them. Look up the words in a dictionary to see the basic meaning, but understand that there are no definite rules that tell you when to use them. Learning them will happen naturally as you're exposed to more examples of English.

At: for a certain point or time "see you at 4" ·"see you at the corner" In: For an specific place "In Rusia people are awesome" For: To tell the use of something "chairs are for sitting" / to tell time o duration of something "I´ve been waiting for 1 hour" / to direction of something "this is for you" Of: Belonging "The hardest part OF english is its grammar" / for references "That is a bag OF mine" "That is a selfie OF a year ago" From: to tell where something comes from "This is a gift from me to you"

Hi Sonya, just a correction to your question. It should read, "When do we use at, in, for, of, from, the and a?" I understand what you mean to ask by "when used...?" but it's incorrect in English. I'd follow Paulette's advice and look them up. It's even better to find real examples - you'll get a more natural understanding of the prepositions and articles that way.