We give a presentation of Feynman categories from a representation-theoretical viewpoint.Feynman categories are a special type of monoidal categories and their representations are monoidal functors. They can be viewed as a far reaching generalization of groups, algebras and modules. Taking a new algebraic approach, we provide more examples and more details for several key constructions. This leads to new applications and results.The text is intended to be a self-contained basis for a crossover of more elevated constructions and results in the fields of representation theory and Feynman categories, whose applications so far include number theory, geometry, topology and physics.Organization of the text. The text is designed to be as self-contained as possible and is aimed at a diverse audience.We start in §1 with collecting classic results for groups and quiver representations, but reformulated in categorical language. This presentation might be of independent interest as a primer.The next paragraph, §2, contains the definition of Feynman category introduced as a special type of monoidal category. The representations are then given by strong monoidal functors. The development is parallel to that of §1. The presentation of indexed Feynman categories is new. The section ends with examples which are based on finite sets. Here we provide new details. The representations of these are various kinds of algebras. The group(oid) representations are also included as a basic example. Further examples are provided by graphical Feynman categories. The theory of graphs we use is detailed in Appendix A.We then turn to various constructions for Feynman categories in §3. These yield Feynman categories whose representations are lax-monoidal or simply functors. At this level the finite set based Feynman categories have FI-modules and (co)-(semi)-simplicial objects as objects. The next operation is that of decoration. It yields the graphical Feynman categories that encode operadic-types, see Table 7. The next construction is the plus construction. Here we give a detailed exposition of the condensed presentation in [KW17, §3.6], providing several explicit calculations. The new precision yields gcp-version of the plus-construction, which is a generalization of hyper version contained in [KW17, §3.7]. The relationship to indexing is also made more explicit here then previously. A detailed graphical based analysis is given in Appendix B, where we also give a careful discussion of levels.In §4 we tackle the enriched version. This is technically the most demanding and contains many new details. The bar/co-bar transformation and a dual transformation, aka. Feynman transform along with the master equations are discussed in §5. Traditionally the bar/co-bar adjunction can be used to define resolutions. For this one needs a model structure in general. The relevant details are reviewed in Appendix D. The W-construction is reviewed in §6. Here we also reconstruct the associahedra in their cubical decompositions.We end the paper with an outlook, §7...