here is a link that tells you what to expect with the US military.

Entering the Military ? Today's Military

every ones experience is a bit different depending upon why they are enlisting, which career they are enlisting for, for example someone entering the military with a goal of mechanics (garage work on vehicles/ planes/ ....) will have different training process then someone who's goal is to become a soldier on the front lines vs someone who enters with the goal of being a medic.

for some people boot camp is easy and for others its hard. example someone who was great at high school PE activities like rope climbing, balancing, jungle gyms and track and field will have an easier time then those who did not excel in high school PE class.

for some people the testing process is easy and for others its hard depending upon ones education and performance anxiety with test taking.

for some people the medical exams part of the process is easy and for others its hard depending upon how well someone is at handling being naked in front of their peers, going to the doctors, showering with others of the same gender ...well you get the point.