What is thyroid adenoma? Will it cause weird stuff to happen to me?

Depends. Thyroid adenoma is a growth on your thyroid. 95% of these growth are benign (not cancerous) and if it's small (< 1 cm), it typically will not cause any problem. If you have a thyroid adenoma, you should get your thyroid blood test done to make sure the thyroid is still functioning normally. A biopsy can also be done to rule out cancer process in the growth.
Yes or no. An adenoma can be either functional or nonfunctional. If it is nonfunctional then it is unlikely to cause you any problems. An exception would be if it was extremely large. A functional adenoma could produce high levels of hormone and make you have hyperthyroidism with symptoms of sweats, diarrhea, palpitations, and tremor.