こんにちは (Konnichiwa) JohnH197,
Both of these verbs mean “to put” or “to place,” but they are used a little differently.
置く (Oku) is used to express putting something somewhere. This can be anywhere, whether it's underneath something, on top of something, behind something, or inside something. For example, “I put the book under the table.”
It implies putting something somewhere for an extended period of time. Imagine buying a new TV and “putting” in your lounge. Since it's not likely that you'll be moving it any time soon, you can express this using 置く (oku).
載せる (Noseru), on the other hand, is much more limited in usage. You can only use this to talk about placing something ON TOP of something else, for example “I put the book on the shelf.”
It implies putting something somewhere TEMPORARILY. Think of it as how you might “put” you coffee mug on top of your car while you load everything inside. You only place it there momentarily until you have all of your things sorted, then move it again.
載せる (Noseru) can also mean “to publish,” as in an article in a magazine or newspaper, or even a photo on your social media account.
I hope this helped! Please let me know if you have any other questions.
勉強を頑張ってください！ (Benkyō o ganbatte kudasai!)