A common topic in a level 1 Spanish class is indefinite and definite articles (el/la/los/las & un/una/unos/unas). Of course, this by needs involves some exploration of grammatical gender as it applies to nouns - and then how this affects article selection.
This handout is the set of notes I give my level 1 students as we begin to explore noun articles and gender. It describes the difference between definite and indefinite articles, and then also instructs students how to determine the grammatical gender of a noun by looking at the end of a word.
This is, of course, a simplified explanation, appropriate for level 1 students (for instance: it doesn't get into why words ending in -ama or -eta are masculine, due to Greek origin. This would be appropriate for more advanced learners, but for this level I treat these as "irregulars.")
I hope this is as helpful for your learners as it has been with mine!