Questions & Answers about Мы рылись в старье и разглядывали безделушки.
Because the subject is мы = we.
In the Russian past tense, verbs agree in gender/number, not in person the way present-tense verbs do. Since мы is plural, both verbs take the plural past form:
- рылись = we were rummaging / we rummaged around
- разглядывали = we were looking at / examining
So the -ли ending is the normal past plural ending.
The dictionary form is рыться, a reflexive verb.
Here, -сь is just the short reflexive ending attached after a vowel. After consonants, you usually see -ся; after vowels, often -сь:
- рыться
- рылись
In this verb, the reflexive ending does not mean a literal ourselves. It is simply part of the verb рыться, which means to rummage around, dig through things.
So рылись should be learned as the past plural form of the whole verb рыться.