Just opened shopify store&new domain, Want to start PPC, currently sell on ebay, no idea about PPC.

PPC can be a deadly expensive game. But it is a totally reliable qualified traffic driver. You have a large enough catalog to be able, most likely to do some long tail search. Skip the big obvious words, e.g., "men's pants" or whatever.That won't help much.

I would look into Google & Bing Shopping Campaigns - those ads appear for most-product specific queries - but be careful with your spend. Obviously, you need to track performance closely, it is the only way to run PPC. But as the former CMO of an Internet Retailer Top 500 fashion company - I think that your profit margin is really, really tight. Typically, most fashion retailers are working with 45%++ margins and have deep enough pockets to break-even on the 1st transaction - but for you with only $5-7 in profit per transaction, you are going to have find REALLY cheap clicks. (Assuming 3% conversion rate - you are going to have to drive 230 clicks for less than $7 to break even - that is $0.03/click - I haven't seen that in Google for over a decade)

Here is a blog post I wrote on long-tail keyword modeling - it might be helpful: Long Tail Keyword Modeling | Selling To The C. Maybe you can work content marketing really hard to create better organic traffic...and perhaps you can invest some money into PPC to drive your e-mail list...