Learn Russian: Улица длинная и красивая.

The conjunction и simply means "and". We use it to connect things that go together or add information, like listing two positive qualities of the same street. You would use а if you wanted to contrast two different things, like "This street is long, а (while/but) that street is short."

Where is the word for "is" in this sentence?

In Russian, the present tense of the verb "to be" (am, is, are) is almost always skipped. So, to say "The street is long", Russian literally just says "Street long" (Улица длинная).

Why do both длинная and красивая end in -ая?

Adjectives must match the gender of the noun they describe. The noun улица (street) ends in -а, which makes it a feminine word. Because of this, both "long" and "beautiful" take the standard feminine adjective ending -ая.

Could I change the word order to Длинная и красивая улица?

You can, but it changes the phrase from a full sentence into a descriptive noun phrase. Длинная и красивая улица just means "A long and beautiful street." Because Russian doesn't use the word "is", putting the noun first (Улица длинная...) is how you create the "The street is..." meaning.