Please help me with any info on my Giant Rainier, serial number GK287424; it was gifted to me recently.
Giant sold a model with this name from 2005 to 2012, so it's a relatively-early 29" hard tail with a triple crankset and quite-decent components. It is not a BSO or walmart-grade of bike.
There was some redesign in 2006, according to https://products.mtbr.com/product/bikes/xc-hardtail/giant/rainier-363498.html
For more general info, start by googling the brand/model and "review" like this https://www.google.com/search?q=review+giant+rainier
If you have more specific questions, ask a new question (with clear photos ideally)