What computer specifications mean
Central processing unit (CPU)
This is the part that executes the instructions in the software. The central processor (CPU) in personal computer systems used primarily for email, web browsing, word processing, spreadsheets, etc., reached a point of diminishing returns a very long time ago but the companies who make the processors and the companies who sell new computers don't want you to know that. Don't let them convince you to throw away money for processing power you'll never use. Unless you run software that does math you don't need the latest and greatest central processor no matter what it says in the advertising you read.
For most people, the most important performance factor in personal computers has nothing to do with CPUs. It's about storage devices. No matter how much memory they have, computers constantly read data from storage and write it back out. Slow storage devices such hard disk drives can't keep up with even a relatively inexpensive CPU. Solid-state drives have no moving parts and are roughly 10-15 times faster than hard drives.
What do Core i3, i5, i7, i9, etc. mean?
They're brand names of Intel processors. It's important to understand that a brand name such as i7 without a generation name or number means very little. Generations are code names applied to various series of Intel Core 64-bit processors that evolve and improve over time. Don't assume that a computer with an i7 CPU is faster than one with an i5. An older generation i7 may be considerably slower.
Is the Intel nomenclature a scam?
In my opinion, yes. Sellers use Intel brand names, particularly i7, to fool consumers into thinking that they're getting something they're not. Intel does absolutely nothing to educate the public about its nomenclature to prevent this sort of deliberate misinformation.
Graphics processing unit (GPU)
The graphics processor (GPU) and the amount of video memory are important if you run games or other graphics-intensive software. 1GB of GPU memory is enough for "casual gaming" but if you want to play the latest games at the highest settings, you need at least 2GB.
Some laptops have two graphics processors with automatic switching. When idle, the system uses a processor-integrated GPU for video playback and other less-demanding tasks. It's more energy efficient than a high-performance GPU. For complex 3D gaming, a dedicated GPU takes over and provides significantly greater performance but runs much hotter.
Memory size in gigabytes
Don't buy a system with 4GB of RAM. You won't like it. 8GB is usually enough for laptops that are used primarily for email, web browsing, word processing, and simple spreadsheets. 16GB allows you to do more things at the same time. For example, some people keep many windows maximized all at the same time. Almost every software product installs memory-resident code for product updates, helper applications, etc. Those don't use much but they add up over time. You can always upgrade your memory to the hardware limit.