Trying to code an ETH transfer in HTML for my website. Can anyone help?

So firstly I thought it would be necessary to say that I have little-to-no coding experience. This is really my first time being exposed to a lot of these concepts.

I found this bit of code online.

It seems to work almost flawlessly, but I ran into two problems.

Firstly- I need to specify the amount of ether being transfered. (I plan on the value being 0.1ETH). I am aware that the code says "// amount: '0xfe'; – add if you want to", but I tried to delete the // and replace '0xfe' with '0.1' and it seemed to have broken the code.

Secondly- The transaction seems to operate on the Rinkeby Test Network, and I need some help changing the network to the Ethereum Mainnet.

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Thank you all for the help!