A tablespoon is a non-scientific but very widely used unit of volume, which works very well in cooking, herbal medicine, etc. It is represented by a capacity of one tablespoon which varies from roughly 15 mL in the US to 20 mL in Australia.
1 If tea is properly stored, it can potentially last up to a year for green and black teas. White tea lasts about six months before it isn't as good in quality as when fresher. Stale tea (or bad tea) will taste flat, as if you're drinking paper.  Glass or ceramic containers are fine provided that they're opaque.
These smaller pieces are more prone to oxidation and turning stale. Your best bet is to buy tea bags in quantities that you think you can use up within six months, so that the flavor and aroma remain strong, and before it becomes a bit more stale after one year. Add a note to the container holding the stored teabags when you bring them home, so you know how long to keep them.