I don't understand it all, even though I witness it.
The alien people effect physical contact with us (and each other race to race) in many different ways by the use of technologies and natural abilities.
One way meetings are "physical" is by use of dimensional technologies.
They can be standing in the next dimension on their crafts in their suitable artificial atmosphere.
They can land their crafts right over (through) where you are, and in effect, stand right next to you and allow you to see them by use of additional technologies (or by your own natural abilities).
You may have some awareness of the affects of the technologies, but all you would see is the alien person seemingly with you where you are.
Out of Body
Another way is when you are out of body, but don't know that you are, and you meet with the alien people as they are in their own environment.
Some of the races that visit Earth can actually be all right in our atmosphere physically with the use of chemical aids for a very short time, but this is dangerous and not taken on lightly.
It is easier and safer to just use dimensional technologies or to visit out of body.
I have never seen an alien in a space suit on Earth.