The video above contains a 12-minute long explanation from Khan academy covering the basics of area and perimeter. This is by far the best video I could find using the metric system, as it does a good job of explaining the meanings of both area and perimeter and the differences between the two. However, Khan does make two mistakes in the video. The first one is an addition error (!) in the video at about 4:20, when he says 8+8+8+8 is 36 instead of 32. ALSO, there's another mistake at about 9:20 where he gives an area as "centimeters" instead of "centimeters squared". Even maths teachers make mistakes. :)
The above video contains a very clear explanation about how to find the area of triangles.
The area of an object cannot be compared to its perimeter - perimeter is measured in units of length, but area is measured in units squared.
Objects with the same perimeter can have different areas.
Area does not equal length plus width.
Study and practice
Use these search terms to find additional resources:
area of square
area of rectangle
area of triangle