but I don't know hw to use them to move my servomotor.
Well, just sending them to the serial monitor is useless, as you've observed.
You need to make use of the data. Exactly how to do that depends on what the data on the card looks like.
If there is a continuous stream of characters that represent digits, you have a problem. If there are non-digit characters in between, like carriage return, line feed, space, etc. then those form delimiters.
You can store the characters in an array, and use atoi to convert the array to an int, then reset the array. Or, you can construct the int as you read each digit from the file.