A normal bond yield curve is a downward sloping curve. As rates rise (x-axis), the price falls (y-axis). Its not a straight line due to convexity which means the price change is greater for a given change in yields when yields are low than when yields are high. In contrast if you have a callable bond, you basically have a bond plus a short call option. The issuer can exercise the call if yields fall to the point where the bond price is greater than par at the call date. This means the price is capped. From the standard yield curve, this means the curve flattens horizontally at the low yield end. A putable bond is a bond with an embedded long put option. This means if yields rise sufficiently, the bond holder can exercise the option and sell the bond back to the issuer at par. From the standard yield curve graph, this means there's a price floor starting at a sufficiently high yield so the curve flattens horizontally at that end.