“I want to thank you for all the support you've given me.”

You're leaving your company to start a new job. You visit your boss to say goodbye on your last day. You want to show that you appreciate how she has helped you. You tell her:

I want to thank you for all the support you've given me during my time here.

I want to (say something)

This is a way to introduce something you want to say in a formal way. You can use it for both positive and negative statements. An example of a negative use is when you have a complaint that you want to make to a company that you are a customer of. You can start by saying to the manager:

I want to complain about the lack of service I received.

give (someone) support

To "support" someone means that you help them. It can also mean that you will help them if they need help.

You can give monetary support, which means that you will pay for someone to live or do business. Another kind of support is emotional support, which means that you listen to someone's problems and give helpful advice. One other kind of support is physical support, which simply means that you help to hold someone up so that they don't fall down.

When you're talking about one specific thing that someone does for you, you can say:

Thanks for supporting me.

But when you're talking about how someone has supported you repeatedly over time, you can use the phrase "give ___ support":

She's given me a lot of support over the years.

You can also use "give support" when you want to explain what kind of support it is - monetary, emotional, or physical.

all the (something)(someone) has (done)

When you want to discuss things a person has done, you can use this structure:

My dad used to tell us about all the beautiful women he had dated before he met my mom.

All the unsuccessful businesses she's started in the past have taught her a lot about running a business.

my time here

This phrase means the entire time that you spent somewhere - at a company, at a school, in another country, at a summer camp, etc. It's usually used when you are leaving that place or situation. Like when you are leaving your job, you can say:

I really enjoyed my time here.

It's a slightly formal phrase.