Every bold outlined section must contain the consecutive integers from 1 to the quantity of cells in that section inclusive.
If two identical numbers appear in the same row or column, at least that many cells with other numbers must separate them. For example, two cells both containing '1' may not be orthogonally adjacent, but must have at least one cell between them with a different number. Two cells marked '2' in the same row or column must have at least two cells with other numbers between them in that row or column, and so on.
The numbers represent the height of the skyscraper in each cell. The clues along the edges tell you how many skyscrapers you can see from that vantage point.