The phrase "couple sentences" means writing or speaking only a few sentences to convey information or an idea. It refers to a small amount of text or speech containing two or a few sentences. Full definition
You'd figure it out after the first couple sentences in the paragraph, but after a bit it became a little irritating. (goodreads.com)
Read each section carefully and be sure to give as much information as you can.In the «talk about yourself» section be sure to have more then just a just couple sentences. (netbest10.com)
I recommend glancing over the pictorial of the this workout below before reading the next couple sentences so that everything makes sense — it's not a complicated structure, but explaining it with words is harder than showing you. (pumpsandiron.com)