Euclid's 5th Postulate says - " If a straight line falling on two straight lines makes the interior angles on the same side of it taken together less than 2 right angles then the two straight lines , if produced indefinitely, meet on that side on which the sum of angles is less than two right angles ".
For example - a line , say PQ falls on lines, say AB and CD such that the sum of the interior angles 1 and 2 less than 180-degree on the left side of PQ. Therefore, the lines AB and CD will eventually intersect on the left side of PQ.
seems boring ??? Try it out yourself make the diagram
i m open for any other query