Questions & Answers about Маленькая снежинка села мне на лоб и сразу исчезла.
Because it describes снежинка, and снежинка is:
- feminine
- singular
- nominative case (the subject of the sentence)
So the adjective has to agree with it:
- маленький — masculine
- маленькая — feminine
- маленькое — neuter
- маленькие — plural
Here, маленькая снежинка means a small snowflake.
Russian nouns have grammatical gender, and nouns ending in -а / -я are very often feminine. Since снежинка ends in -а, it is feminine.
That matters because other words have to match it, for example:
- маленькая снежинка
- снежинка села
- снежинка исчезла
Both past-tense verbs are in the feminine singular form because the subject is feminine.