Start with 3 one-by-one squares. This represents the '3' in 4t+3
Then draw 4 rectangles that are vertical or horizontal. Make sure the rectangle is longer than it is wide, or vice versa. The longer side is t units long (t is just a placeholder for a number). The shorter side is 1 unit long
The longer thin rectangles have an area of 1*t = t square units. Four of them represent t+t+t+t = 4*t = 4t
The small squares have an area of 1*1 = 1. Three of them represent 1+1+1 = 1*3 = 3
This is one possible way to draw it out. See the attached drawing.