Learn Russian: Его дедушка умер.

The perfective aspect is used here because dying is a completed, one-time event that has a final result. If we used the imperfective form умирал, it would mean was dying, focusing on the ongoing process rather than the final result.

Дедушка ends in -а, which is usually a feminine ending. Why is the verb умер in the masculine form?

Even though дедушка (grandfather) ends in -а, it refers to a male person, making it a masculine noun. Verbs in the past tense must match the natural gender of the person, so the verb takes the masculine form умер instead of the feminine умерла.

Most past tense verbs I have learned end in -л (like читал). Why is there no -л at the end of умер?

Умер is an irregular past tense form. Some Russian verbs drop the -л ending in the masculine past tense if the root of the word ends in a consonant. However, the feminine and plural forms still keep the sound, as in умерла (she died) and умерли (they died).

Why is Его pronounced with a v sound instead of a g sound?

In Russian, the grammatical endings -его and -ого are always pronounced with a v instead of a g. This is a very common pronunciation rule you will see in possessive words like this one, which means his.