basicly read the posts in this section and you should find what it can and can't do.
Basically the other posts should cover the basics.
Going deeper - is there anything in particular you are wondering about? LDAP is basically a protocol used to access directory services - which are often compared to databases.
If you are comparing it to a relational database you will find that directoy services are better optimized for searches both in performance and with the flexibility of how searches can be defined, has much more granular access control mechnisms, and can be distributed much easier with the built in replication functionality and ability to design the namespace to break out different portions of data based on locality requirments or SLA's.
Drawbacks would be the lack of transaction support for most products (though I believe IBM does support this with their offering) and very little capability to ensure data is correct once it has been entered (though some referential integrity is possible). Additonal constraints would be the poorer performance for write transactions as well as some restrictions on size of data elements that should be stored.