“Isolate”: Separate live virus from everything else until you have a sample of live virus that you can use to infect cells in the lab, then grow new virus in those cells to produce new samples of just the virus and nothing else. It’s hard to with viruses and we often don’t bother.

“Identify”: Take a swab from a someone’s nose, sequence all the dna and rna in it, see what we find. It’ll be mostly snot and human dna, but any viral rna will show up and can be compared with the rna sequences from the viruses in other samples.