As you’ve discovered, there are many different Jewish prayer books (siddur, plural: siddurim). Each one reflects the beliefs and practices of the particular Jewish community for which it is intended. For example, contemporary Reform siddurim avoid gendered language that refers to God or to worshippers.
Different denominations within Judaism use different prayer books, and within Orthodoxy, prayer books reflect the unique customs of various cultures, sects, and ethnic groups. There are prayer books for weekday, Shabbat, and holiday worship, with specific prayers, readings, and rituals for those days. The prayer book for the High Holidays is called a machzor (plural: machzorim) and is published as a separate volume. In addition, some synagogues publish their own prayer books.
Look for a siddur that includes both English and Hebrew, as well as transliteration. Transliteration – Hebrew written out in English letters – will help you follow the Hebrew prayers that are recited or sung in synagogue.
Mishkan T'filah, the Reform Movement’s newest siddur, includes Hebrew with both transliteration and English translations, as well as beautiful prayers in English. If you are exploring Judaism with a rabbi or cantor or participating in a congregation, it’s a good idea to ask which siddur the congregation uses in communal worship.