mind that hardwood and softwood have two mutualy exclusive grading standards. So, when you go to the big box and look for the odd hardwood board the construction lumber grades you may be used to don't apply. Here is a simple primer on hardwood grades
https://www.woodworkerssource.com/shop/grad.httpHere is a much more detailed guide with various specie/grade photographs
https://www.esf.edu/wus/documents/Illus ... gGuide.pdfThe second page might be a good keeper for reference before you go to the wood stock for lumber.