provide assistance to (someone)

"Assistance" means "help". "Provide" means "give". So "providing assistance" to someone means helping them.

One way that we use "provide assistance" is to talk about organizations that give money to groups to help people like disaster victims, people with disabilities, and so on:

Donations will go to provide assistance to families displaced by the recent earthquake.

You can also use "provide assistance" to describe helping someone in very formal speech. For example, if you are a witness in court, you might describe helping someone to the judge like this:

I saw a vehicle parked on the side of the road with its warning lights on, so I stopped to provide assistance. 

a disabled (person)

A "disability" is some kind of problem with a person's body such as:

• blindness
• deafness
• a missing arm or leg
• a mental disability

A person who has one of these problems is called "disabled"

If you want to be very careful not to offend someone with one of these problems, you might use the term "differently abled" instead of "disabled". However, not everyone accepts this term because some people think that it's silly to be so careful about what we call people in this group. 

a veteran

A "veteran" is someone who has been in the military or fought in a war.

Veterans are sometimes identified by the war that they fought in:

a World War II veteran