Yiddish is spoken as a daily language in some parts of America, mostly in New York City, and in some parts of Europe, particularly Eastern Europe, and South America, as well as in Israel. It is slightly higher than standard German, with a large admixture of words of Hebrew, Slavic, or other origin. As Yiddish is roughly 75% Germanic in origin, German speakers can understand a large part of it.
Yiddish is written with the same alphabet as Hebrew, with a few additional letters, and is written from right to left.
Yiddish pronounciation is different from German or Israeli Hebrew. Words of European origin are spelled out, similar to most European languages, and can be said as they are spelled. On the other hand, words of Semitic (Hebrew and Aramaic) origin are written just as in the original Hebrew or Aramaic, without vowels. In many cases you must learn how to pronounce these words in Yiddish; you cannot necessarily work it out from their spelling, and they are mostly pronounced differently from Israeli Hebrew.
Take note that most native speakers do not use most of the diacritical marks. For example, both "אַ" and "אָ" are usually written as "א". While "ײַ" is almost always written as "ײ". In the latter case, this makes sense, as words represented here as "ey" or "ay" are often pronounced slightly differently from dialect to dialect.
Furthermore, "פֿ" is almost always written as "פ", because there is a dot in "פּ" to distinguish it.
The dots used to distinguish "ייִ" from "ײ" are often replaced with an "א" as in "װאו" rather than "װוּ" which is somewhat clumsy visually.
All these differences represent standardised YIVO orthography versus the more widely employed "Modern Standard", other variations exist.
א shtumer alef
silent; used before ו vov and י yud when they are vowels; e.g. איר (ir) you subj.
אַ pasekh alef
אָ komets aleph
like volume; only used in words of Hebrew or Aramaic origin
like or or tune
וּ melupm vov
used in place of ו vov when it appears beside װ tsvey vovn
װ tsvey vovn
ױ vov yud
like the Scottish Gaelic loch, German ach, or as in חנוכּה (khanuke); used only in words of Hebraic or Aramaic origin
like yet (as a consonant) or internet (as a vowel)
יִ khirek yud
used beside another vowel instead of י yud, to show that it is to be pronounced separately; e.g. ייִדיש (yidish) Yiddish
ײ tsvey yudn
ײַ pasekh tsvey yudn
like keep; used only in words of Hebraic or Aramaic origin
כ ך khof
מ ם mem
נ ן nun
פֿ ף fey
צ ץ tsadek
like coo, but further back in the throat
voiced gargle as in French, can be pronounced as root
like seem; only used in words of Hebrew or Aramaic origin
like teeth; only used in words of Hebrew or Aramaic origin
like smooth; only used in words of hebrew or aramaic origin