Long-time ebay seller here. Shipping is actually quite easy. You need two tools - a scale and a tape measure. If you're only selling a handful of items, don't bother with a scale but if you're going to be selling a fair amount, get one. You can get a really nice one for under $25. Here's the one I use:
https://www.amazon.com/dp/B00KYA0RC2?psc=1&ref=ppx_yo2ov_dt_b_product_details
Once you know the size and weight of your package, ebay will calculate shipping for you or you can do it yourself at USPS.com, PirateShip.com, or ShipStation through PayPal. If you are selling on ebay, you do not want to just take your package to the post office and have them weigh and label it because you get a substantial discount if you do it online.
You mentioned fragrances. Be aware that perfume is classified as a hazmat item. It can only be shipped USPS Ground, not Priority or any service that goes by airplane.
Offering "free shipping is just a gimmick since there is no such thing. If you want to do that, make sure you price your item accordingly to include the shipping cost.
Personally, I don't care if an item is $20 plus $10 shipping or $30 with "free" shipping. Either way I pay the same amount. But some people don't do math well and they'd rather buy the item with "free" shipping. Some even filter their searches to only show items with free shipping which is stupid but it's apparently a thing folks do. I do not offer "free" shipping on my items because I don't believe in playing that game.
Small heavy items are best shipped through PirateShip.com because they do cubic Priority and you can't get that anywhere else. For everything else I use USPS though really big items are usually best through UPS. I just don't sell any of those. USPS also just added a steep surcharge on long items like golf clubs so UPS is best for those now.
Feel free to message me if you have any questions or need help with anything, especially on ebay. There are also great Facebook groups for sellers on the various platforms (ebay, Mercari, Poshmark, etc.).