I'm new to this group, so I apologize in advance if there is a post
already done on this ( I couldn't find it).

My husband is not able to help with this project due to a disability,
but my house windows on the back side & some on the front side at the
bottom corners, I noticed, have turned brown and black and some have
holes in it.

When I poke my fingers in it, the wood is hollow. I suppose it's water
damage which has rotted out the inside of the outside window sill.

I would like to replace them and want to do it myself to save money;
however, I cannot find any step by step instructions showing me how to
do this. Also I'd like to ensure that the windows were properly
installed to begin with, such as a flashing etc.

Can anyone offer any assistance.

Thank you,
Billie Goodman