The most common way to express gratitude in English is to say "Thank you." "Thanks" is an abbreviated form of "Thank you." Gratitude can be expressed in many other ways in English. Depending on the situation, the level of formality may be important.
The ways of expressing thankfulness can range from informal to extremely polite. "Thanks a million" and "Thanks a ton" are very informal. "I am forever beholden to you" and, "You have my gratitude" are more formal.
Other expressions of gratitude are, "I can't thank you enough" and, "I truly appreciate it." Both of these expressions can be used in a formal or an informal situation.