The MCL Mangai layout is neither fully phonetic (unlike "Tamil Phonetic") nor purely positional (unlike "InScript"). It is a where vowels and consonants are assigned to keys based on a mix of logical mnemonics and frequency of use.
Begin typing using the typewriter mapping. If you don't have the layout memorized, you can use the to see which keys trigger which Tamil characters. Quick Reference Table English Key Tamil Character (Approx.) q a s d f mcl mangai tamil font keyboard layout