Used: Husk; sometimes the whole seed
For those who want the minimum information, here is a summary:

For constipation,5 to 30 gram per day with plenty of water, one hour separated from taking medicines.

For every gram of psyllium take a minimal 30 ml of water

For further information read below.

Helps constipation, and when soft stools are important, for example, after anal surgery and surgery for fissures, and haemorrhoids and during pregnancy 

Psyllium is also used as extra help for hyperlipidemia [high cholesterol]

The husks should be taken with plenty of liquid [take for every gram of the herb 30 ml water]  to prevent intestinal obstruction and far from the time when supplements or medicines are taken, at least one hour as it may bind with the medicines and prevent their absorption  

Psyllium contains mostly water-soluble fibres and mucilages [=slimy substances]
It increases the volume of intestinal contents which helps in defecation and the slimy substances help to make the deflection smoother

Ispaghula should not be taken within at least  one hour of any other medication, as it may delay their absorption

 The total daily dosage: 5 to 20 gram, at once or divided over the day Effect can be expected after12 to 24 hours after taking a single dose, maximum effect after 2 to 3 days.  Don;t forget: Take for every gram of the herb 30 ml water.

The herb is safe![but don’t use if you had complicated intestinal surgery or intestinal obstruction]