The word הָיָה means “to exist” or “to be” or “to become” or “to come into being” and occurs 3561 times in the Old Testament.

This is the foundational verb of existence, identity, becoming and occurrence.

• It is used in the creation narrative of Genesis 1, represented by the English words “Let there be” (Genesis 1:3plugin-autotooltip__default plugin-autotooltip_bigGenesis 1:3
  
  Hebrew וַיֹּ֥אמֶר אֱלֹהִ֖ים יְהִ֣י א֑וֹר וַֽיְהִי אֽוֹר ESV And God said, “Let there be light,” and there was light. NIV And God said, “Let there be light,” and there was light. NLT Then God said, “Let there be light,” and there was light. LXX καὶὁθεόςφῶςκαὶφῶς)
• God also connects his name with הָיָה when he says that “I AM has sent me” (Exodus 3:12plugin-autotooltip__default plugin-autotooltip_bigExodus 3:12
  
  Hebrew וַיֹּ֨אמֶר֙ כִּֽי אֶֽהְיֶ֣ה עִמָּ֔ךְ וְזֶה לְּךָ֣ הָא֔וֹת כִּ֥י אָנֹכִ֖י שְׁלַחְתִּ֑יךָ בְּהוֹצִֽיאֲךָ֤ אֶת הָעָם֙ מִמִּצְרַ֔יִם תַּֽעַבְדוּן֙ אֶת הָ֣אֱלֹהִ֔ים עַ֖ל הָהָ֥ר הַזֶּֽה ESV He said, “But I will be with you, and this shall be the sign for you, that I have sent you: when you have brought the people out of Egypt, you shall serve God on this mountain.” NIV δὲὁθεὸςλέγωνὅτιἔσομαιμετὰσοῦκαὶτοῦτόσοιτὸσημεῖονὅτιἐγώσεἐξαποστέλλωἐντῷἐξαγαγεῖνσετὸνλαόνμουἐξΑἰγύπτουκαὶλατρεύσ…)
• The word is frequently used to mean “and it came to pass”, e.g. Ruth 1:1plugin-autotooltip__default plugin-autotooltip_bigRuth 1:1
  
  Hebrew וַיְהִ֗י בִּימֵי֙ שְׁפֹ֣ט הַשֹּׁפְטִ֔ים וַיְהִ֥י רָעָ֖ב בָּאָ֑רֶץ וַיֵּ֨לֶךְ אִ֜ישׁ מִבֵּ֧ית לֶ֣חֶם יְהוּדָ֗ה לָגוּר֙ בִּשְׂדֵ֣י מוֹאָ֔ב ה֥וּא וְאִשְׁתּ֖וֹ וּשְׁנֵ֥י בָנָֽיו ESV In the days when the judges ruled there was a famine in the land, and a man of Bethlehem in Judah went to sojourn in the country of Moab, he and his wife and his two sons. NIV In the days when the judges ruled, there was a famine in the land, and a man from Bethlehem in Judah, together with his wife an…
• And the word is used by the prophets to announce “it shall come to pass”, e.g. Isaiah 2:2plugin-autotooltip__default plugin-autotooltip_bigIsaiah 2:2
  
  Hebrew וְהָיָ֣ה בְּאַחֲרִ֣ית הַיָּמִ֗ים נָכ֨וֹן יִֽהְיֶ֜ה הַ֤ר בֵּית יְהוָה֙ בְּרֹ֣אשׁ הֶהָרִ֔ים וְנִשָּׂ֖א מִגְּבָע֑וֹת וְנָהֲר֥וּ אֵלָ֖יו כָּל הַגּוֹיִֽם ESV It shall come to pass in the latter days that the mountain of the house of the LORD shall be established as the highest of the mountains, and shall be lifted up above the hills; and all the nations shall flow to it, ὅτιἔσταιἐνταῖςἐσχάταιςἡμέραιςἐμφανὲςτὸὄροςκυρίουκαὶὁοἶκοςτοῦθεοῦἐπτῶνὀρέωνκαὶὑψωθήσεταιὑπεράνωτῶνβουνῶνκαὶἥξουσ…

The most common forms of היה in the Old Testament are:

• Root: היה (h-y-h)
• A Qal verb most of the time
• Other stems (like Niphal and Hiphil) are rare or have slightly different meanings

In Exodus 3:14, God says to Moses:

• אֶהְיֶה אֲשֶׁר אֶהְיֶה
• “I AM who I AM” (or “I will be what I will be”)

Here the verb אֶהְיֶה is the 1st person imperfect of היה, meaning “I am” or “I will be”

Note that God's personal name YHWH likely is related to the same root היה, which emphasizes God's being, existence and faithfulness.