Is my sentence correct?

[arzgol]

You have you pull yourself up on a rock using your hands and feet.
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I'm a little confused with the word "rock'', because sometimes it is
uncountable and sometimes countable. Could you please explain it to me.

Thank you for speanding your time answering my question.

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[SoothingDave]

He's climbing on a particular rock. It's not referring to "rock" as a type of substance. So it is a rock. Where people go rock climbing there are usually numerous rocks in the landscape.