You can buy clothing with the morphs already built in.  That is the easiest way.  Many of DAZ's clothing packs come with a lot of morphs.

You can adjust the clothing yourself, using magnets.  There's a bit of a learning curve, but it's a very useful skill to have.

You can buy a utility such as The Tailor or Wardrobe Wizard, which will fit the clothing to morphed figures.  They are pretty easy to use, though the results are not always ideal.

If  you're using Poser 5 or 6, you can use dynamic clothing, which can be easily fit to any figure.