By and until are two prepositions that are used in the English language. These words will come before a noun or a pronoun. By gives a deadline. An example is "John and Kate ask that we be at the chapel by 7 pm". In this sentence, 7 is the deadline. It could also indicate direction such as "He is by the house." Until it is the period of time before the deadline, an example is "He has until 8 pm EST to turn in his paper or he will fail the class" here, until it is used to describe the point before action needs to occur.
You would normally use “by” and “until” when you know that you need to use prepositions. These are prepositions of time, and they are commonly misinterpreted. When you say “by,” this is a preposition that means that you are giving a deadline for something. For example, you might say, “Please submit the article BY April 15.” This means that the article should be submitted on or before the said date.
When you say the word “until,” this means that you are focusing on the time before the said date, for example, you can say, “Prepare the different requirements needed to submit the paper until April 15.” This means that people will be given the time to prepare the requirements before the said date.