IVF involves several steps. First is ovarian stimulation, you'll be given medication (contains Follicle Stimulating Hormone) that will ignite multiple egg production per month. Next are egg and sperms retrieval, and then fertilization outside of your body and finally embryo implantation.
If you are have damaged or blocked fallopian tubes, suffering from endometriosis, or not able to conceive due to age related issues, then you should go for IVF.
No, the process is not painful.
Generally a cycle of IVF is about 2months.
IUI has lower success rate than IVF. IVF is the most reliable and successful infertility treatment.