Could anyone please help me improve this and help me with the conclusion?

Very interesting, but as a teacher, some of your sentences are run-on (they lack commas and flow) and others are too choppy. For example, your first sentence might sound better as "Although different genres of music came and went throughout the early 1900s, Rock and Roll was introduced in the 1950s and has stayed popular in America ever since." I would also use a thesaurus for words like "different" and "many." Your conclusion should restate your topic and sum everything up using the same information you used in your paragraph. Again, it is very interesting, but just needs minor tweaks.