Here is the info on mulch in general:
https://extension.umd.edu/resource/mulching-trees-and-shrubs
and specifically for veggies gardens:
https://extension.umd.edu/resource/caring-your-vegetable-garden-maryland

Personally, I use heavy duty landscape fabric (porous) on my walkways, held down with landscape fabric pins. It has been there for many years. This is not the "inexpensive" weed barrier type. After a few years, weeds may start to grow on top of, or through the fabric. Cardboard or several sheets of newspaper are also options, but they last for only 1 season and must be held down with bricks, rocks or pins.

For the beds, wait until the seedlings are 2-3" tall and start to have "true" leaves before mulching. Also, for warm weather crops, wait until the soil warms.

I do not use mulch on my vegetable beds since sanitation is important to minimize disease and insects. However, in the spring, you can top off the beds with 1" or so of compost (Leaf Gro) or aged manure (read product instructions).  If you want to use mulch, 1-2" of pine bark "fines" will work and degrade over 1 or 2 years to improve the soil. 

There are pros and cons to other mulch types for veggie beds. I'd stay away from using hardwood mulch (which mats) and larger pine nuggets, grass clippings (unless dried first and not treated with any herbicide), straw (unless guaranteed to be weed free) or plastic products (which can overheat the soil in the summer), or newspaper or cardboard (can prevent water penetration). 

Good luck,
Len