You would think this is the easiest kanji in the whole language, it certainly is to write. However, reading is a little trickier. It tends to be いち ichi one, but there are also some words where it is pronounced as ひと hito one, depending on the combination of kanji. There are even あてじ ateji special readings, still meaning one. Of course, students can misread it in katakana words where the dash means long sound.
Here are examples of the most common words:
一々 いちいち ichi-ichi one by one, separately
一番 いちばん ichiban number one, the first
一番搾り いちばんしぼり ichi-ban shibori the first pressing
一日 いちにち ichi-nichi one day long
Here: one word a day in English conversation. By the way, that still means only 365 words in a year, which isn't all that much. Anyway, you get the idea. They mean steadily.
However, 一日 can also be pronounced as ついたち tsuitachi and then it means the first day of the month.
Every first day of the month is the first day of being connected.
一日中 いちにちじゅう ichi-nichi-jū all day long
Today too, I'll have to do my best all day long.
一年中 いちねんじゅう ichi-nen-jū all year long
ice-cream all year round
一才 いっさい i-ssai one-year-old
one-year-old cherry tree
一時間 いちじかん ichi-jikan one hour
a one-hour special with Doraemon character. Yeah!
However: on signs 一時 いちじ ichi-ji one hour 停止 ていし teishi doesn't mean stopping for an hour. It means you just HAVE to stop. Oh well, traffic for you.
一時 いちじ ichi-ji one o'clock
一年 いちねん ichi-nen one year
A year has passed since then.
一月 いちがつ ichi-gatsu January
一ヶ月 いっかげつ i-kkagetsu one month long
一枚 いちまい ichi-mai one sheet, flat object of something
one flat zabuton cushion
一度 いちど ichi-do one time, once
一度 いちど ichi-do one degree, 1℃
もう一度 もういちど mō-ichi-do once more, one more time
One more time ONLY YOU
一台 いちだい ichi-dai one car, one machine
These cars are eco-cars
一輪車 いちりんしゃ ichi-rinsha mono-cycle, wheel-barrow
一円 いちえん ichi-en one yen, 1 yen
一千円 いっせんえん i-ssen-en one thousand yen, 1000 yen
一万 いちまん ichi-man ten thousand, 1,0000
一万円 いちまんえん ichi-man-en 1,0000 yen banknote
一億 いちおく ichi-oku 100,000,000; one hundred million
一人 ひとり hitori one person, alone
一人っ子 ひとりっこ hitorikko an only child
Don't let it upset you - there are many more words. However, they all mean one thing or another.