Like the previous few grammar points, いらっしゃる is also a 尊敬語（そんけいご） (honorific) expression. Thich means that it elevates the status of another person, in order to pay respect. It will never be used when referring to the speaker themselves, or their actions.
いらっしゃる can be used to replace 居（い）る ‘to be’, 来（く）る ‘to come’, or 行（い）く ‘to go’. This is due to the unique perspective that 尊敬語（そんけいご） places the speaker in, in relation to the person that is being respected. This is a slightly advanced concept that we will discuss more later.
To use いらっしゃる, simply replace いる, くる, or いく with いらっしゃる.

• あなたの隣（となり）にいらっしゃるのはお嫁（よめ）さんですか。
  Is the person next to you your wife?
• あと30分（ぷん）で社長（しゃちょう）がいらっしゃるので準備（じゅんび）をしてください 。
  The CEO is coming in 30 minutes, so please get ready.
• 先輩（せんぱい）は明日（あした）の忘年会（ぼうねんかい）にはいらっしゃいますか？
  Senpai, are you coming to the end of year party tomorrow?

Alternatively, いらっしゃる may also be used to replace いる, くる, or いく when they are attached to the て-form of another verb.

• 田中様（たなかさま）が来（き）ていらっしゃたので案内（あんない）をお願（ねが）いします。
  Mr. Tanaka is here, so please guide him (to where he needs to be).
• マユミさんはタクシーに乗（の）っていらっしゃるのでもうすぐ着（つ）きます。
  Mayumi-san is coming by taxi, so she will be here soon.
• 今日（きょう）は歩（ある）いていらっしゃいそうです。
  It appears as though he will come by foot.