Numbers in Hebrew have feminine and masculine forms, so they need to match the gender of the noun that they modify. The numbers usually appear immediately before the nouns, with the number one being an exception.
If we are simply counting, the feminine form is used. Feminine is also used for telephone numbers, bus routes, and telling time. Here, let's look at a chart with the basic 1-10.
Number/transliteration Feminine (counting) Masculine (“ah" ending)
One אחת...ah-CHAT אחד...eh-CHAD
Two שתים...sh'TAY-eem שנים....sh'NAY-eem
Three שלש...sha-LOSH שלשה...sh'loh-SHA
four ארבע...AHR-bah ארבעה...ahr-bah-AH
five חמש...cha-MESH חמשה...cha-mee-SHA
six שש....shehsh ששה...shee-SHA
seven שבע...SHEH-vah שבעה...shee-v'-AH
eight שמנה...sh'MOH-ney שמנה...sh'moh-NAH
nine תשע...TAY-shah תשעה...tee-sh'-AH
ten עשר...EH-sehr עשרה...ah-sah-RAH
*I regret that I cannot insert the niqqudot (vowel pointings) to facilitate reading for beginners, but I hope that you can at least see that the masculine is formed by adding a hey ה, to the feminine. This is the “qametz-hey”, making the “ah” sound in the final syllable of the word.
This is sort of backwards from what you may know about Hebrew gender in the words. Usually, an “ah” ending is indicitive of a feminine noun. Well, with mispareem, (numbers,) it is the opposite! Aמ “ah” ending is the masculine form of the number!!
In numbers one and two, simply remember that the form with a tav, ת, is the feminine. (ah-CHAT, sh'TAY-eem)
Note also that both feminine and masculine number “two” have what I call the “dual endings”, with the patach-chireq dipthong, and emphasis on the second syllable (the syllable with the patach). See March 21. 2012 blog on Hebrew plurals for more on dual plurals (things occuring in pairs)
NOW: Try counting in Hebrew a few times!
AND HAVE FUN!!!
*The list of numbers with niqqudot are found on page 195 in the text: First Hebrew Primer, which I use for my Advanced Biblical Hebrew classes.