I have 2 Unmanaged switches (100Mbps) and I want to replace them with one switch like this, which is 1000Mbps but it is managed. The TL-SG2452 is plug & play or I will have to do a setup in order to work?
If you just plug it on the network without touching anything on the configuration it should behave just like an unmanaged switch.
This happens because the stock configuration generally allows this. If the switch have VLAN capabilities it come for example with a predefined VLAN1.
But do yourself a favor and at least learn how to connect to it and explore its features. If you like networking you'll be pleased.
The basic switching functionality will be there right away. This means normally all ports are enabled and assigned to the same default VLAN (usually 1). Further, usually there is Spanning Tree active by default.
So long story short: You can use the switch right out of the box, you however have the possibility to add and configure other features (for example VLANs, basic routing, security features, or other things) as required.