Normally speaking in tongues is something that happens in the context
of worship. I've never heard of it done in one's sleep and I would tend
to be skeptical that it is genuine speaking in tongues, though
I have experienced it in unusual circumstances (though not quite so unusual)
so I suppose I can't rule it out.
You won't necessarily understand what you were saying. There are some
cases in which you or someone else may have a gift of interpreting what
you say in tongues (see 1 Cor 12:10,30; 14:5,13,26-28), but often it is
uninterrupted. Interpretation of tongues is something akin to the gift
What does it mean for you? It may merely be a gift that builds up your
faith, that assures you that God is there and that he loves you. It could
allow you to pray ecstatically, or at least pray when you don't know what
to pray for (see Romans 8:26).
Some say speaking in tongues may involve speaking on the tongues of angels
(1 Cor 13:1). Others point out that angels, being pure spirit, have no
tongues and need no language to communicate (or at least, wouldn't communicate
as we do). One important thing though is not to get too enamored of tongues.
You'll notice that this is what happened to the Corinthian church, which
was the most unruly and immature of the communities St. Paul wrote to.
A dose of humility is always wise.
How do you talk to God? I see four ways to talk to God. First, talk to
him from the heart, extemporaneously, as a friend. Share your concerns,
feelings, and needs with him. When that fails you, or if it doesn't provide
enough structure, pray in the words of other people, for example, the Psalms.
The ideal way to do this is by praying what's known as the Liturgy of the
Hours, which is the private prayer book of the Catholic church. It can
be done by any person anywhere. You can also find rote prayers that you
like and pray those. You can even construct your own fixed prayers in your
own words. The third way to talk to God is not to talk at all but to meditate,
that is, to think about God, to wordlessly offer him your heart and show
him affection, to gaze upon him warmly.— Here an icon or Eucharistic
adoration is helpful. Lastly, there is speaking in tongues.
I hope this helps!