Steem tokens are tradable tokens and can be bought or sold instantly at anytime. It does not determine how much influence you have on Steemit.

Steem power are long term shares of a company that when invested in, can only be cashed out at 1 percent per week, over 2 years. A total of 104(number of weeks in 2 years) payments over 2 years. Investments in Steem power means the commitment to the long term value and health of it.

Each Steem dollar can be converted to Steem worth 1 dollar. It's pegged to the US dollar. Currently convertible to Steem worth about 80 cents and ranges from 80 cents to $1.40 the highest so far I've seen. And the range is sometimes dependent on the price of Steem going up or down when converting. But ultimately it's convertible to Steem worth 1 dollar.