"You walk and I run."
Translation:bIyIt 'ej jIqet.
This is explained in the Tips and Notes.
After choosing a lesson unit, instead of clicking on Start, click on the little lightbulb icon next to it instead -- that will take you to the Tips and Notes. After reading them, you can then start learning that unit by choosing the Start button at the top of the Tips and Notes page.
Joining two nouns is explained in the Tips and Notes for the first unit, https://www.duolingo.com/skill/kl/Useful-phrases/tips-and-notes (section Joining nouns with and without "and"), and joining two sentences is explained in the Tips and Notes for the first unit on the second row, https://www.duolingo.com/skill/kl/Sentences-1/tips-and-notes (section Joining two sentences with "and").
Would "I walk, run and jump" be "jIyIt, jIqet 'ej jISup"? Two parts to this question - does the prefix have to be included for each verb (rather than, for example, "jIyIt, qet, Sup je"), and do lists of verbs therefore never use "je" (because there is always a subject or implied subject)?
I agree that every verb has to have a prefix and I also favor putting an 'ej between every pair of sentences, though I think we have evidence of a list of sentences with 'ej only before the final one and some klingonists definitely believe that's the more appropriate method.
However, I have no problem also putting je after a sentence that is already connected by 'ej to give an "and also" type of emphasis.
You are using lowercase L, but in this sentence each of those is an uppercase i. It is unfortunate that in the Duolingo font they look so similar, but if you look closely you can see the small curl at the bottom of the l that distinguishes it from the I. Getting used to where an l might appear in a syllable and where an I might appear is one of those hurdles that makes beginning to learn Klingon challenging. Until you get familiar with the patterns you will have to look carefully for the presence of absence of that curl.