Every time you click on an item within your email design, the Properties Panel on the right-hand side will display the relevant settings & options; different for each item selected.
If you want to change the Font, font size, and colour of the text box you have, clicking on that text box will show you the relevant settings in this menu. For example, increasing the font size, and aligning it to the center will give you a header for your email, which would contrast between the body text you might have below it.
In the particular case of text boxes, you'll also notice the menu along the top, which is important for hyperlinks, bold/italic text, and bullet point lists among other options. Using this menu along the top will allow you to select certain words, and not affect the entire text box, as you may want to only place a hyperlink on a certain word, or bold only one line of a paragraph for example.
For Hyperlinks in particular, in the Properties Panel you will find the different options for putting colours on your linked text. And you can change that colour based on if the link is hovered over, as shown in the screenshot here.
Experiment with the options found in the Properties Panel and you'll find all the settings you could want for editing your email content!