Blood glucose levels vary a lot. How high or low they are on average, is being determined by many factors. For example, though not limited to:
Normal blood sugar levels range between 3.9 mmol/L and 5.5 mmol/L. We are talking about blood sugar levels in a fasting state, i.e., when waking up after a night sleep and not having eaten yet. Do note, that based upon the above factors, this can differ without anything to worry about (i.e., it can be lower than 3.9 mmol/L without any issues. Also see our dedicated article about this).
After a meal, a healthy blood sugar level should stay below 7.2 mmol/L. Again, changes may occur based upon the above reasons. When you peak too often above this value, you have a higher risk for health related issues such as overweight, obesity, inflammation and diabetes type 2. Peaking every now and then is not by default a health concern, though you want to avoid these moments. For example: do you peak from candy, and do you eat this rarely or daily? That matters a lot.
Besides the range, it is important how quickly your blood sugars increase (i.e., the steepness of the curve). The steeper the curve, the bigger the chance you gain weight and feel fatigued (the so-called after dinner dip).