How to handle concurrent write/read to a db

Hi all,
in my application i have two databases. lets call them a & b.from database a i will be just reading data and displaying it to the user.no writing has to be done.but on database b i have to perform writing as well as reading operations.since multiple users will be accessing this database i have a few questions
i) how do i take care of the cuncurrency issue?
ii)will the cuncurrency issue come in only when two users try to write something to the database at the same time or is it a problem even when multiple users try to read at the same time?
iii) should i implement connection pooling?i dont expect a lot of cuncurrent users(around 50 or so).is there any threshold value for the no. of concurrent users beyond which it is advisable to implement connection pooling.
Thanks in advance.
Subbu