I agree with most of the above, but for clarification would add that while "ı" is similar to schwa (the unstressed vowel sound that occurs in many English words, such as in an unstressed "the" or the last syllable of "warren"), it is not identical. Some books describe it like the vowel sound of "put" said with spread lips (I'm not sure how useful that is!) If you are familiar with phonetics, then "ı" is a close back unrounded vowel; it's IPA symbol is /ɯ/.
The pronunciation of "ğ" depends, to some extent, on whereabouts in Turkey you are, but in Istanbul Turkish, it normally serves to lengthen any preceding "a", "ı", "o" or "u", while it is realised as a "y" sound (/j/) after "e", "i", "ö", or "ü". One exception is in words derived from the verbs "öğretmek" and "öğrenmek", where it does not have this "y" sound.
"Ö" is pronounced the same way in German as it is in Turkish, or, if you are familiar with French, it is similar to "eu", and, in fact, that is how Turkish words containing "ö" are transcribed in older French books.