# Assembling¶

In this section of the tutorial the user can learn how to assemble the linear system associated with the finite element discretization of the Poisson problem. First of all, we proceed by defining the finite element space (**FESpace**) and then we show how to assemble the stiffness matrix and the right hand side (RHS) by means of the Expression Template Assembler (**ETA**). In the last subsection, we give some details about the degrees of freedom (**DOFs**) and the data structure (map) used to manage them, in particular how to treat the map for parallel runs.

- Creation of the FESpace - In this tutorial we show how to define the finite element space
- Assembling the linear system - In this tutorial we show how to assemble the linear system
- Maps - In this tutorial we talk about maps, i.e., the data structure used in LifeV to store the degrees of freedom