It's a similar mistake to saying "I reads" in English. You may be understood by someone who is sympathetic to the struggles of learning a language, but you will definitely sound foreign!
About the worst mistake you can make with the wrong verb conjugation is to say sie lesen instead of sie liest, for example. This changes the meaning from "she reads" to "they read". Because it doesn't sound obviously wrong, it's likely that you'd be misinterpreted.
There is a very slight connotative difference in English, (-s is present perfect tense and is -ing is present progressive tense) but German only has a single present tense. So from German to English, both translations are correct and you would pick the preferred form using context.
Although the Rheinish dialect does have a progressive aspect, in standard Hochdeutsch the best you'll get is the adverb gerade following the verb. In that case using present progressive tense is a preferred translation.
They just need to match with different 'people', like how in English it's "I read" but "he reads" and you can't swap them around. This modification of verbs to match the 'person' is called conjugation, and is one of the basic challenges of learning many languages. You'll find patterns as you learn.