Siman 550
Presented here for study, not as a practical ruling. The Shulchan Aruch rules by Sephardi custom, the Rema's glosses by Ashkenazi custom, and the Kitzur follows Ashkenazi custom. For a practical question, ask your rabbi.
א הַכֹּל חַיָּבִים לְהִתְעַנּוֹת אַרְבַּע צוֹמוֹת הַלָּלוּ וְאָסוּר לִפְרֹץ גָּדֵר. הַגָּה: מִיהוּ עֻבָּרוֹת וּמֵינִיקוֹת שֶׁמִּצְטַעֲרוֹת הַרְבֵּה, אֵין לְהִתְעַנּוֹת (הַגָּהוֹת מַיְמוֹנִי וְהַמַּגִּיד פ"ה); וַאֲפִלּוּ אֵינָן מִצְטַעֲרוֹת, אֵינָן מְחֻיָּבוֹת לְהִתְעַנּוֹת אֶלָּא שֶׁנָּהֲגוּ לְהַחְמִיר; וְדַוְקָא בְּג' צוֹמוֹת, אֲבָל בְּט' בְּאָב מְחֻיָּבוֹת לְהַשְׁלִים כְּדִלְקַמָּן סי' תקנ"ד סָעִיף ה'.
1 The (legal) distinction that there is between Tisha B'av to the other fasts, and in it there are 4 paragraphs. All are obligated to fast on these Four fasts, and it is forbidden to break the fence (i.e. not fast) Rema: However, those who are pregnant or nursing that are very distressed, do not fast [Hagaos Maimoni and the Maggid Chapter 5]. And even if they (the above) are not distressed, they are not obligated to fast, rather customarily they are strict. (This lack of obligation for those in a lack of distress) is specifically on the 3 fasts, but Tisha B'av, they are obligated to complete (the fast) [like that brought in Siman 554 Paragraph 5]
ב צוֹמוֹת הַלָּלוּ, חוּץ מִט' בְּאָב, מֻתָּרִים בִּרְחִיצָה וְסִיכָה וּנְעִילַת הַסַנְדָּל וְתַשְׁמִישׁ הַמִּטָּה, וְאֵין צָרִיךְ לְהַפְסִיק בָּהֶם מִבְּעוֹד יוֹם.
2 These fast except for Tisha B'av one is allowed to wash, anoint, wear shoes, and have marital relations. And it is unnecessary to stop (from eating) when it is still day (in the case the 3 fasts when it is still night and the fast has not started yet).
ג כָּל ד' צוֹמוֹת הַלָּלוּ אִם חָלוּ לִהְיוֹת בְּשַׁבָּת, נִדְחִין לְאַחַר הַשַּׁבָּת. הַגָּה: וְאִם חָלוּ בְּעֶרֶב שַׁבָּת, קוֹרִים בְּשַׁחֲרִית וּמִנְחָה, וַיְחַל (בֵּית יוֹסֵף); וְאִם יֵשׁ חֻפָּה בְּיוֹם הַתַּעֲנִית בְּעֶרֶב שַׁבָּת, נוֹהֲגִין לְהִתְפַּלֵּל מִנְחָה וְלִקְרוֹת וַיְחַל וְאַחַר כָּךְ עוֹשִׂין הַחֻפָּה וְעַיִּןִ לְעֵיל סי' רמ"ט (סָעִיף ד') אִם מַשְׁלִימִין הַתַּעֲנִית.
3 All four fast if they fall on Shabbos, they are pushed to after Shabbos. Rema: If they fall on the eve of Shabbos, we read in the morning and afternoon prayers the parsha of Vyachel (Exodus 32:11 and on) [Bais Yosef] If there is a wedding on the day of the fast on the eve of Shabbos, the custom is pray the afternoon prayers and read Vyachel and then afterwards do the Chuppah ceremony [see Siman 249 Paragraph 4 if one completes the fast].
ד בְּשַׁבָּת קֹדֶם לַצּוֹם מַכְרִיז שְׁלִיחַ צִבּוּר הַצּוֹם, חוּץ מִט' בְּאָב וְצוֹם כְּפוֹר וְצוֹם פּוּרִים וְסִימָנָךְ: אָכַ"ף עָלָיו פִּיהוּ וּמִנְהַג הָאַשְׁכְּנַזִּים שֶׁלֹּא לְהַכְרִיז שׁוּם אֶחָד מֵהֶם.
4 On Shabbos before a fast, a Community Representative (Shaliach Tzibur) announces the fast except for Tisha B'av, Yom Kippur, and the Fast of Purim (Taanis Esther). The remainder is forces (אכ"ף - Aleph - tisHA bav Kof - yom KIppur Geh - Purim) on him his mouth. (see Proverbs 16:26) Parentheses the custom of Ashkenazim is not to announce even one of them (of the fasts).