"Those people are young."
Translation:Ty osoby jsou mladé.
masculine animate nouns - ten pes (singular nominative) -> ti psi (plural nominative) [the dog-the dogs]
masculine inanimate nouns - ten strom (sg. nominative) -> ty stromy (plural nominative) [the tree-the trees]
feminine nouns - ta žena (sg. nominative) -> ty ženy (plural nominative) [the woman-the women]
neuter nouns - to město (sg. nominative) -> ta města (plural nominative) [the city- the cities]
ta osoba (feminine sg. nominative) -> ty osoby (feminine pl. nominative)
You really need to read the Tips & Notes and/or use another reference like, for example, the site linked below, where you can find out how any word changes depending on its gender, number, and (for nouns, pronouns, and adjectives) case, and (for verbs) tense: https://en.wiktionary.org/wiki/mlad%C3%BD (click Declension if you don't see the table). But the Tips & Notes should be especially helpful to you in the early stages of your Czech learning adventure.
If you have no previous experience with an inflected language -- briefly, one that makes those kinds of changes -- learning Czech could be very challenging, especially in the beginning. But it can be done if you have patience and the dedication to continue with it.
Absolutely, the Tips & Notes are not optional reading but required so you don't get lost, and one simply must learn what is in them. Learning them will speed your learning curve; avoiding them will undoubtedly slow your progress down. The explanation above about ti, ty, ty and ta, those are in one of the Tips & Notes.
I was a self-defense instructor for a long time long ago. It is the same way. You must be truly proficient in the level where you are before you proceed higher, otherwise you carry your mistakes with you into the higher belt, which unavoidably slows down your overall progress because then, at some point, you have to take all this valuable time to undo that and relearn things correctly. But how do you remove all those faulty actions, conclusions, mistakes from your brain as well, because retraining does not catch all things, all images. Lay down the most solid neural net in your brain as possible and try not to allow mistakes and doubts to linger for long because they will definitely be recorded in the brain. Thinking mice have many more neural lines in the brain than lazy mice who don't do puzzles, mazes, tricks to get their food. Thinking wrong also creates neural lines in the brain. I have degrees in psychology, as well as in self-defense, so glad to share this. Use it as you are able.
I'm starting to add in my notes like on this sentence, f.pl. to reinforce the genders. The previous one, Ti lide' jsou mladi' I added "m.pl." and then I just think through it correctly each component matching it to that correct gender, and then I move on. If that helps others, great. I'm using my iphone. I found out it will accept all these czech words (without accents as I'm using English on the phone) once I tap it in and then select it where it gives you three choices, then after the second time it's used, the phone doesn't try to switch it to some English word. I'm gonna see about switching the phone to czech and find out if that's got no problems it introduces. It may do speech recognition for Czech then, but not do it any more for English. I don't know.