Glad that you found this site which has the best information of everything you'd need to know about budgies. Make sure you read all the "stickies" relative to care, health, and taming + the forum.
Your budgie is very new and for now the best thing to do is allow him to settle in and not fuss with him. Make sure he has seed and water available and spend time with him but do not handle him. Just let him adjust to his new environment. Green poop is not a good sign, but it could be he's not eating enough and is afraid. Budgies will bathe but you should not "give him a bath". It seems that in bathing him, he was overly wet and until his feathers dry, they tend to stick together, like I see in the photo. As soon as he dries off his feathers should look normal. Don't try the bath again. Budgies will bathe themselves if they want to. The best thing you can do is relax and make sure that you are not directly touching or handling him. He needs time to adjust. If he continues to have loose greenish poop you should have him see an avian veterinarian who specializes in treating birds. Welcome to Talk Budgies and good luck with your new friend.