To re-share an existing post on memestr, click on the three dots next to the post you want to share, and select "Share" from the dropdown menu. From there, you can copy the link and share it on your preferred social media platform or messaging app.
As for buying a fraction of a bitcoin, you can use a platform like Coinbase or Binance, which allow you to purchase small amounts of bitcoin. Another option is to use a service like Swan Bitcoin, which allows you to buy fractional shares of bitcoin. Just be sure to do your research and choose a reputable platform to ensure the security of your investment.