Learn English – what with — what does that actually mean

There is no "general context" meaning of the word; the word "claim" can have one of many meanings depending on its context. As for your example:

I will claim the amount.

The word "amount" suggests to me that money is involved, and therefore I can assume that the meaning is this one (as per dictionary.com):

to demand by or as by virtue of a right; demand as a right or as due: to claim an estate by inheritance.

Thus, if you claim an amount, you declare that you have a right to that amount.

The use of the meaning of jots and tittles is kind of the same as in the dictionary, but different. As @TRomano has pointed out it can mean markings for typesetting, however C is notorious for using what the author in your excerpt is terming small symbols that have very significant meanings.

The same would be true for punctuation in writing. Commas (','), periods ('.'), question marks ('?'), exclamation points ('!') all convey different meanings. Consider the differences between

Hello.
Hello!
Hello?

The so called "jots and tittles" referred to by the author of your passage can be thought of as (a kind of) punctuation for the C language.

For example

. (period character)

is used to reference part of a data structure

something_struct.name

a = something_struct.name;

however, if one only has a pointer to the structure and not the actual structure one would use

a = pointer_to_something_struct -> name; (spaces added for clarity)

To define a block

{ ... } (curly brackets/braces)

if (my_condition){
do something;
} else {
otherwise do something else;
}

other languages like Python implicitly use indentation instead.

For conditional compilation ( C is a compiled language )

# (hash character)

#include
#ifdef
#ifndef

Each "line" of code ends with

; (semicolon)

One of the intentions of the curtness of the syntax was to avoid keystrokes and it's low-levelness was a result of basically being a step up from assembly language (as low as you can go). It also borrows concepts from Unix.

Most of the more "modern" languages are built on C (probably since C was there first): Python and Ruby are examples of this.

C is a great language, however, it is very low level and if you want an abstraction, you have to make it yourself(!) It is therefore very pedantic, which might not be to everyone's taste.

With all due respect for the series of books, C is not for dummies, and the reference to jots and tittles is as appropriate or inappropriate as if it was used to refer to punctuation in grammar.