How to create custom variables in wordpress

Have a look at the get_user_meta function.

Assuming the litecoin address in the user’s profile is stored as user meta, with the key of litecoin_address you can output the link like so:-

$litecoin_address = get_user_meta( get_current_user_id(), 'litecoin_address', true );

if( !empty( $litecoin_address ) ){
    // maybe do some additional sanitation of the litecoin address here
    $link = sprintf( 'http://free-liteco.in/?r=%s', $litecoin_address );
    echo $link;
} else {
    echo 'Please login and complete the litecoin address in your profile';
}