1.  Use Paypal Shipping.  It's cheaper than the post office. 

2.  You need a scale.  I recommend THIS one.  I've used it for YEARS without any issues.  (If you don't want a rose gold one - get THIS one instead) 

3.  These are labels I use.  They work in my regular printer and stick on my envelopes so easily  

4.  These are the bubble mailers I use.

For 1-2 bottles of oil I use THESE

For larger shipments I use THESE

5.  If you need a printer - I LOVE THIS one.  It's super inexpensive.  It's wireless which means I can print from my laptop/phone/ipad anywhere in my house.

A couple of tips:

With PayPal shipping - You'll want to select First Class shipping for anything under 16oz.  If it is more than that, it's great to compare the price of your package to a flat rate envelope/package when bumping up to priority.  You can take these flat rate envelops/boxes from the post office.