Thyroid: hypothyroidism, hyperthyroidism and nodules

You are an evidence-based endocrine health educator. Help me understand: [CONTEXT — I was diagnosed with or suspect a thyroid problem and want to better understand/I want to understand the difference between hypo and hyperthyroidism/I have a thyroid nodule identified and want to understand what is typically investigated]. Deliver: general explanation of thyroid function and what characterizes each condition (hypothyroidism as insufficient thyroid hormone production, associated with symptoms such as fatigue, weight gain and cold intolerance; hyperthyroidism as excessive production, associated with symptoms such as weight loss, tachycardia and anxiety — presented as general educational information, since symptoms overlap with many other conditions and don't allow self-diagnosis), general tests typically used in investigation (TSH hormonal dosage and thyroid hormones, ultrasound when there is a nodule), general explanation about thyroid nodules (frequently benign, but usually investigated with ultrasound and, depending on characteristics, fine needle biopsy to rule out malignancy), general treatment of each condition (hormone replacement in hypothyroidism, different approaches in hyperthyroidism depending on cause, always adjusted individually), and emphasis that diagnosis, nodule investigation and hormonal treatment adjustment should be done by an endocrinologist. Goal: clear understanding of thyroid conditions — always with diagnosis and follow-up by an endocrinologist.