@nonsense73, since the correct writing of tengwar relies heavily on proper placement of the tehtar (vowel marks) above the characters, there are four different keys for each tehta. This plus the fact that there are several different characters that don't have exact English equivalents mean that matching each character to an English letter would not work very well.
Instead, this is set up in a grid pattern based on Tolkien's layout in the books. Here's a character map for tengwar fonts. https://quenya101.files.wordpress.com/2011/10/tengwar-keyboard-layout.png
As far as I know, all tengwar fonts follow this setup. So you can't really type in it without knowing the script, but that shouldn't be a problem for you, since you speak Quenya.
@meepin, I don't know if you're still wondering after so long, but if anyone else wants to know, the placeholder character is the "tilde" key next to the 1. Normal for short vowel, shift for long vowel.