Can someone please explain this to me using plain language… When we record the bond at amortized cost and the bond was purchased lets say at a discount-what does it mean to change the bond value on the B.S to amortized cost. Supposed YTM =10% Coupon= 9% purchased @ 900 FV + 1000

I’m not sure what you’re asking, but that’s probably because you’re not sure what you’re asking. Are you asking for the high-level overview or the actual math? That bond is going to mature and pay out 1000, right? If you bought it at 900 then the accountants would like you to get closer to the 1000 over time. That difference of 100 is dealt with through amortization (accretion is the correct term when you buy the bond at a discount) and is recognized over the remaining life of the bond.