When 切る is attached to another verb's ます-stem, it adds the meaning of doing that action thoroughly, completely, or until the very end. It often implies that something is used up, finished, or overcome with effort. For example, 読み切る means to read something all the way through, and 疲れ切る means to be completely exhausted.

This pattern is often used with verbs that involve consumption, completion, or endurance. It can also carry a nuance of finality or extremity, like 困り切る (to be at a complete loss). In many cases, it suggests that the action was difficult or required reaching a limit.

In spoken Japanese, you'll hear it in contexts where someone finishes a large task or uses something up entirely. It's not overly formal, but it is more common in writing or in deliberate speech than in casual chat. For a lighter, more conversational way to say 'finish doing', you might use 終わる instead.