If

"If" is אִם im. For something that may happen, the if-clause takes the tense it means; for the future, both halves take the future, unlike English. אָז az "then" may start the second half.

• אִם יֵרֵד גֶּשֶׁם, נִשָּׁאֵר בַּבַּיִת.
  im yered geshem, nisha'er babayit
  If it rains, we'll stay home.
• אִם תִּרְצִי, נֵלֵךְ לַיָּם.
  im tirtsi, nelekh layam
  If you like, we'll go to the beach.
  to a woman
• אִם אַתָּה עָיֵף, לֵךְ לִישֹׁן.
  im ata ayef, lekh lishon
  If you're tired, go to sleep.
  to a man

What isn't so

For something that isn't so, or wasn't, both halves take a past form of הָיָה and a present form: הָיִיתִי קוֹנֶה hayiti kone "I would buy, I would have bought". The same words serve for now and for the past.

• אִם הָיָה לִי כֶּסֶף, הָיִיתִי קוֹנֶה דִּירָה.
  im haya li kesef, hayiti kone dira
  If I had money, I'd buy an apartment.
  a man speaking
• אִם הָיִיתָ בָּא, הָיִיתָ נֶהֱנֶה.
  im hayita ba, hayita nehene
  If you had come, you'd have enjoyed it.
  to a man

Formal Hebrew uses אִלּוּ ilu or לוּ lu for this "if".

I would like

הָיִיתִי רוֹצֶה hayiti rotse, or רוֹצָה rotsa for a woman, is a polite "I'd like".

• הָיִיתִי רוֹצָה לְהַזְמִין שֻׁלְחָן לִשְׁנַיִם.
  hayiti rotsa lehazmin shulkhan lishnayim
  I'd like to book a table for two.
  a woman speaking

Whether, even if, unless

אִם also means "whether": אֲנִי לֹא יוֹדֵעַ אִם הוּא יָבוֹא "I don't know if he'll come". אֲפִלּוּ אִם afilu im is "even if", and אֶלָּא אִם כֵּן ela im ken "unless".

• נֵצֵא, אֲפִלּוּ אִם יֵרֵד גֶּשֶׁם.
  netse, afilu im yered geshem
  We'll go out even if it rains.