He shall from time to time give to the Congress Information of the State of the Union, and recommend to their Consideration such Measures as he shall judge necessary and expedient; he may, on extraordinary Occasions, convene both Houses, or either of them, and in Case of Disagreement between them, with Respect to the Time of Adjournment, he may adjourn them to such Time as he shall think proper; he shall receive Ambassadors and other public Ministers; he shall take Care that the Laws be faithfully executed, and shall Commission all the Officers of the United States.
This clause is a bit of a grab bag of various presidential duties. The president is required to report to Congress on "the State of the Union"; over time, this requirement has taken the shape of a formal "State of the Union Address" delivered every January to a joint meeting of both houses of Congress. The president can call Congress into special session when it's out on recess if he thinks there is urgent business the Congress needs to deal with. The president has to "faithfully execute" the laws of the United States; this is probably the most important part of the presidential job description, so it's a bit odd that it's just tucked into the latter half of this clause. Finally, the president has to grant commissions to all military officers of the United States. See, it's a grab bag, like we said!