OK, so I am creating a game where a UFO flies around. I want some things like its landing pad to be solid, but I can't figure out how. Can someone please help me?

Not enough information.

Please tell me what you mean by “a solid landing pad.”

Look at the sticky topics for platform games. The pad just needs to be a colour or sprite then use the sensing blocks to detect its presence.

I always use these two scripts for decent gravity:

When Flag Clicked:
Forever
Change y by yspeed (yspeed being a variable)

Now for another script:

When Flag Clicked:
Forever
Repeat Until: touching color Black? (I generally use the color black for ground and platforms,
Change yspeed by -1 but a sprite or a different color would work just as well…)
If: touching color Black? then:
set yspeed to 1 (you can change these numbers as needed)

This should work for you; I find it a simple yet effective way to give individual sprites gravity.
Welcome to Scratch, by the way!

if <(platypus) = [platypus]> then
set [platypus v] to [platypus]

Here is an example of something similar to above. http://scratch.mit.edu/projects/12969047/