Computer systems are digital. Programs and data are represented electronically. Digital data is made up of a sequence of bits. The term bit stands for binary digit. A bit can take on one of two values: 0 or 1. Whether information is a computer program, text, numbers, sound, images, etc., it is a sequence of 1's and 0's. The same exact sequence of 1's and 0's could be an instruction, image, number, etc. How it is treated depends on what the computer is doing with the information. For example, if it is writing to the speakers, the data is sound.
Every CPU has a unique instruction set. The instructions are called operation codes. All CPU's have similar instructions. However, the unique binary string for each instruction is different for every CPU.
Programs and data are stored permanently on your hard drive. To execute a program (e.g. Word, browser, etc.), the program must be read into RAM. The data the program is operating on must also be in RAM. RAM holds the programs and data you are currently working on.
Computers execute instructions (programs) that reside in RAM. The CPU reads instructions and data from RAM. Each location in RAM has an address. A byte is made up of 8 bits. While a single bit is the smallest unit in the computer system, individual bits are not addressable by the CPU. The byte is the smallest addressable unit in RAM.
Suppose you have a .docx file stored on your computer containing a report for this class and you want to modify the file. You double click on the file. The OS loads Word into RAM along with your .docx file and launches Word. You then interface with Word to change your file. The changes are made in RAM. When you save the file, it is copied from RAM to your hard drive.
There are codes to represent each letter of the alphabet as well as punctuation, etc. This code is ASCII. ASCII is an 8-bit code. It is the most widely used code for representing text data. Numbers are represented in binary. You have probably only learned the decimal number system. In decimal, you have digits 0-9. All numbers are represented with 0-9. The number 9832 is actually 9*10^3 + 8*10^2 + 3*10^1 + 2*10^0. Each position in the number is a power of 10. The binary number system is similar. All numbers are represented with 0-1. Each position is a power of 2. The binary number 10011011 is 1*2^7+0*2^6+0*2^5+1*2^4+1*2^3+0*2^2+1*2^1+1*2^0.