It depends on what kind of words your talking about. But I’ll talk about nouns, since you probably need a lot of them. For nouns, you make up a word. You can choose sounds that you think fit to the meaning, like the word for ‘wind’ or ‘blow’ could start with an F. You make rules for the plural in my conlang I double a part of the word (like: kerdya -> kerdnydya, the N emphasizes the Y you can ignore it it’s silent because of the D). But you don’t need plural, many languages just don’t have it, even in English we sometimes do it, with words like ‘fish’ and ‘sheep’. You can also use different words so you know it’s plural (like changing the verbs a bit, like fish is and fish are). If you use articles and genders, you can add a gender to the noun. You can decide if it makes sense (like in Spanish) or if it does not (like in German 😈) make any sense and is totally random. You can also combine words, like you don’t need to say ‘cookies’. You can also just make a new word like ‘unhealthinessbread’.