I would actually avoid "can"/"could" when asking something of someone. It will be fine 99% of the time and everyone will understand what you mean but some people are pedantic about "can" being used to ask if something is capable of being done where "will" /" would" is asking the person to do it.

For example if I have a heavy box and I am not sure if you can lift it I would ask "can you carry this box?" in which I want to know if the box is too heavy for you to lift. Where if I already know the person is capable of lifting the box and I want to request help from them it would be more correct to ask "will you carry this box?"

Again it's not a big deal, and even native speakers use the two interchangeably but it's a subtle difference that occasionally can cause confusion.

As for other things :

"Please" for requesting something. You mention using it at the beginning but it can go at the end as well, or even after the subject and before the verb. "please, will you carry this box", "will you carry this box, please", and "will you, please, carry this box" are all fine.

"Thank you " to show gratitude/ appreciation. Just a "thank you" is fine. But if you want to show extra gratitude you can embellish. Stuff like: "thank you, very much", "thank you, I could not have done it without you ", " thank you, you have been such a great help " sometimes adding a little to your thank you can make someone feel more appreciated.

The standard response to "thank you" is "you're welcome" (shortened form of "you are welcome") but you will also hear things like "no problem", "my pleasure", "any time", "it was nothing", or and this one may seem strange "you do not have to thank me". They are all meant to convey that your request was not a burden to them and that they were happy to help you. These alternatives are considered informal but there are no real rules for formal/informal in English "you're welcome" is what everybody is taught and the others people just pick up from use and are sometimes used to add sincerity.

There is also "excuse me" which is used when you need to get somebody's attention. So if someone is blocking your way you can say "excuse me" and they will usually realize they're blocking your way and move. But they also may turn to you and expect you to say more. So "excuse me. Do you know how to get to the train station? " you can also use it to interrupt your own conversation so if you are talking to somebody and you get an important phone call you would say "excuse me, I need to take this call" and then step away to get some privacy.

And "sorry" or "I'm sorry" (I am sorry) which which kind of means the same thing as "excuse me" but is used as a simple apology. So if you bump into somebody at the market a simple "sorry" will be said. They are sometimes used interchangeably but as a guideline I would say "excuse me" tends to be used before you do something that you need to do but feel it would be rude if you didn't tell someone first. "sorry" is used after you do something accidentally.

I hope my explanations didn't confuse you there is a lot of nuance in language that can be hard to describe in asynchronous text. And I didn't add much more than anybody else but sometimes different phrasing can help understand a new concept.