How to read U+ notation
A code point is written as U+ followed by at least four hex digits. U+0041 is A, U+00E9 is é, U+20AC is € and U+1F600 is 😀. The Unicode code space runs from U+0000 to U+10FFFF, split into 17 planes of 65,536 code points each. Plane 0, the Basic Multilingual Plane, holds the most common characters. The range U+D800 to U+DFFF is reserved for UTF-16 surrogates and never holds a character.
The first 128 code points match ASCII, so A has the same number in both.
A code point isn't always what you see
What a reader sees as one character can be several code points. é can be the single code point U+00E9, or e (U+0065) followed by a combining accent (U+0301). Both look the same. A flag emoji is two code points, and an emoji with a skin tone and a joined symbol, like 👩🏽💻, is several. The unit a reader sees is called a grapheme cluster, and it can span many code points.
So length has four honest answers: visible characters, code points, UTF-16 code units and UTF-8 bytes. For 😀 they are 1, 1, 2 and 4. JavaScript's '😀'.length is 2 because it counts UTF-16 units, while [...'😀'].length is 1. Paste any text into the Character Counter to see its code points, UTF-16 units and UTF-8 bytes.
From code point to bytes
A code point is only a number. An encoding decides how it's stored. U+00E9 is the two bytes C3 A9 in UTF-8 and one 16-bit unit, 00E9, in UTF-16. U+1F600 is four bytes in UTF-8 (F0 9F 98 80), and because it's above U+FFFF, a surrogate pair of two units in UTF-16 (D83D DE00). The same text has different byte lengths in different encodings, and reading bytes with the wrong encoding is how mojibake happens.