Contract to receive and pay for a given number of issues of a periodical, for tickets to a series of performances, or for a utility service. For example, We subscribe to the local paper, or Betty and I have been subscribing to this concert series for years, or We have no choice; we have to subscribe to the local power company.
Feel or express approval of, as in I subscribe to your opinion but I don't think Donald does. [Mid-1500s]
Promise to pay or contribute money to, as in We subscribe to many charities. [Mid-1600s] All of these usages come from subscribe in the sense of “sign one's name to something, such as a pledge.”