Hallelujah
Hallelujah is probably the most common of the Hebrew words that Christians use. It is commonly used in songs and other praises. It is a combination of two Hebrew words, "Allelu", which means "praise", and "Yah", which is the short form of the personal name of God. So literally it means "Praise Yahweh" but most people render it as "Praise the Lord".
Some people refer to Hallelujah as the highest praise but that idea does not come from Hebrew. In the Hebrew language it simply means Praise Yahweh. In fact it isn't really a praise at all. For example, think of a pet dog. When the dog does something good for you, you don't say "Praise the dog" you actually praise the dog by saying something like "What a smart dog you are?".
Of course to don't talk to God the way we would talk to a dog. We might praise him by saying something more like "God, I thank you for the way you helped me through that situation. You are truly a wonderful God and wise beyond all measure".
There is nothing wrong with saying hallelujah but don't forget to actually praise God for the things he has done for you.