How do I talk to God when I am completely alone?

Out loud, if you can. Loneliness makes the inside of the head a bad neighbourhood, and speech gets you out of it. Tell God what your day was actually like, in the ordinary words you would use with a friend, including the dull parts. You are not required to make it beautiful or grateful or resolved. Being alone is not a sign that you have been discarded, and saying so plainly — I am lonely and I do not like it — is a real prayer.

The tradition even has a practice for exactly this: hitbodedut — going somewhere alone and speaking to God in your own plain language, out loud, as to a friend.

From the sources “For God alone my soul waits in silence.” — Psalm 62