What is the difference between descriptive and prescriptive

Prescriptive means bound by rules and regulations . For example teachers have a prescriptive attitude towards the knowledge theyimpart to their students. That is to say they abide by the rules of grammar, mathematics etc.

Descriptive is the adjective of the to describe , so it means to relate the features and properties of something .

Descriptive describe.
Prescriptive make or suggest a choice based on some descriptive, but mostly predictive analyses.

A descriptive grammar is built up by analyzing how speakers use a language, and deducing the rules they are following. A prescriptive grammar is a set of explicit rules for using language that are taught, or enforced, so that people will use the language in a particular way. Typically the rules are handed down from generation to generation. Both kinds of grammars have their places in the world.
Linguists create descriptive grammars in order to understand language more deeply. They understand that a single language can have multiple dialects, and that each dialect will have its own grammatical rules--internally consistent, but perhaps different from other dialects of the  same language. The rules they deduce are sometimes more nuanced than the ones taught by prescriptivists.
Prescriptivists include schoolteachers, copyeditors, and others charged with correcting people's use of the language. (Also some people who just have strong opinions on the topic.) Prescriptivists start with the assumption that there is one "correct" way to use the language, and many incorrect ways. The "correct" version is actually the language's prestige dialect, especially its written version--for example, Standard American English. To oversimplify a bit, the "prestige dialect" of a language is generally the one used by educated people in the big cities.