"The sausage has ketchup."
Translation:Το λουκάνικο έχει κέτσαπ.
Yes, but it's tricky. There are several declensions with forms for masculine, feminine and neuter nouns. A greater number of masculine nouns fall under the Ancient Greek second declension and end in -ος or the first declension and end in -ης, while most feminine nouns end in -η or -α and most nouns ending in -ο or -ι are neuter, but there are many exceptions and without knowing what declension a noun is, your best indication is the article which (thankfully) is required. Most nouns that don't conform to the rules in the first link below are loan words, such as κέτσαπ (all loan words are neuter and indeclinable provided that they're inanimate objects). So, for this example, since κέτσαπ ends in π we know it is a loan word and since it's an inanimate object it must be neuter.
cf https://en.wikipedia.org/wiki/Modern_Greek_grammar#Masculine_nouns for the noun declensions
and https://en.wikipedia.org/wiki/Modern_Greek_grammar#Articles for the articles.
έχεις = you (sing.) have
έχει = he/she/it has
What unit are you studying right now? The desktop website of Duolingo has a Tips and notes section under the lessons which is not available on the app or the mobile website. There you can find information about the grammar of each skill so do check it out! For example, verb conjugation tables are available under the Present 1 skill: https://www.duolingo.com/skill/el/Verbs%3A-Present. Alternatively,
Wiktionary often provides conjugation/declension tables https://en.wiktionary.org/wiki/%CE%AD%CF%87%CF%89#%CE%9A%CE%BB%CE%AF%CF%83%CE%B7
Also, check out the sticky posts in the Greek forum with the resources. There are many conjugation tools available online, you'll definitely find one to aid your learning! :)