How would you select part of a letter/font and change the colour of it ??

Here are a few tips to get started:

(1) When you create outlines, hold down the Option/Alt key when you choose Type > Create Outlines. That will make a copy of the outlines which isn't anchored in the text frame. Move that copy away from the original frame.

(2) Select all the word with the Direct Selection tool and choose Object > Path > Release Compound Path. That will separate the letters from each other so you can work with them (it also fills in the counters (centers) of the letters).

(3) To create the effect on the "T," I selected the letter with the Direct Selection tool (selecting all the anchor points) and chose File > Copy, then chose Edit > Paste in Place to make a copy on top.

(4) I moved the top copy a little (Shift + Up Arrow) so I could select the bottom copy, then I locked the bottom copy (Object > Lock). I moved the top copy back (Shift + Down Arrow).

(5) With the Direct Selection tool, I selected the lower anchor points and deleted them. I filled the top anchor points with blue. Here is how far I got: