The SDLC activities of this phase are not necessarily simple, but they are straightforward—install the system and make sure it runs as advertised.
Usually, installation of an IT system is fairly simple, if the components have been built according to the plan and if they have been thoroughly tested. In fact, the integration tests will have required that the components all are connected and working together, so the system has already been installed once. Still, the proof of the pudding is in demonstrating that the system works as the customer expects. So, although this is the only activity in the SDLC for this phase, it is actually the crucial one, because if it doesn't work as the customer expects it to work, then it may be back to the drawing board.
Once the system is installed, the provider tests it to ensure it functions as expected. In addition, the customer is likely to have had a contract clause specifying that he be allowed to operate the system to determine its functionality and adherence to the stated requirements. In fact, this often is the test of acceptability by the customer. Only upon the successful conclusion of this test is the system accepted. But once it is accepted, the whole project is completed and closed. Now a new phase of customer relationship begins—operation and maintenance of the system and continued customer satisfaction.