Promote my website on social media

You could try getting/hiring a virtual assistant to help you promote your website, or try hiring affiliates to help you sell your product. In that case, there will be more customers to visit your site and buy your product.

it depends on your GOAL

wanna use free resources or paid advertising?

I would make a list for both of these niches and do some research into influencers, influencer marketing has worked wonders for gaming and make up - there's no reason why it cant work for fashion. (On a smaller scale as well, don't think PewDiePie, think 'guy or girl that has a humble amount of subscribers but great engagement')

Instagram and Snapchat
You could message them and offer sending them a free tshirt to review or snap a picture of them in to upload.

Youtube
Look for a reasonable amount of subscribers but not so much that they're likely to not even open your email! Ask for a shout out or a tshirt review. Don't be afraid to aim at reasonable accounts! They still have an audience even if its less than 200,000, they are still people with cash and an interest.

Podcasts
Reach out to fashion related podcasts, do a couple of interviews on your personal story. There is definitely opportunity for this on podcasts about fashion+entrepreneurship, think about companies like Hype and Ratchet that used their streetwear clothing as their niche

Pinterest
Get a decent camera or borrow a friends, get some good looking friends or local unknown models to model your tshirts and post them on Pinterest. Tag them appropriately. This can also be content distributed to your FB page and Twitter

Fashion FB Groups
Pretty self explanatory but it's a place to advertise.
Not only fashion groups but music and film groups would be relevant to you too.

Utilise your Niche
Have a rolling stones tshirt? Make sure to advertise your tshirt on one of the dudes birthdays or anniversaries. A star wars tshirt? Celebrate star wars day with everyone on twitter and link to your shirt.
Get what I'm saying?

Make your product relevant to recent news and things happening for the fans of those bands, singers and films.

You can use these social media platforms for promoting your website.

Facebook
Twitter
Pinterest
Instagram
Tumblr

Facebook
Twitter
Pinterest.com/
Stumbleupon.com/

Etsy might work. Pinterest is also good to showcase images of your t-shirts. Try banner advertisements everywhere else (Google Adwords, etc.)

I will suggest you to try FB ads. Before placing ads customize with target audiences, proper interests, and age. Facebook ad is today most cheapest ad in the market now. You can promote your product with as low as 1$ per day. It has a good conversion rates too.
Best of luck.

Why don't you create a Facebook Ads? Facebook Ads is really effective to get targeted traffic. You can customize your Ads on the basis of your targeted traffic. It proves effective for me.

By using Facebook, Pinterest, Etsy, Instagram, Twitter you'll have a success.

Your request actually seems a little vague. Is there something specific that you're having problems with?

Ok, I am just trying social media, it takes me hours but I can't be sure about results yet
Here is my facebook page https://www.facebook.com/sonictshirts if anybody fancy my t shirts please give me a like.
Thanks everebody fot so detailed explanation