1) "Cluster algebras: an introduction" by Williams - https://arxiv.org/abs/1212.6263.
2) "Introduction to cluster algebras" by Fomin, Williams and Zelevinsky - https://arxiv.org/abs/1608.05735.
-The positive Grassmanian:
"Total positivity, Grassmanians and networks" by Posnikov - https://arxiv.org/abs/math/0609764.
1) "Scattering amplitudes and the positive Grassmanian" by Arkani-Hamed, Boujaily, Cachazo, Goncharov, Postnikov, Trnka - https://arxiv.org/abs/1212.5605.
2) "The m=2 amplituhedron and the hypersimplex: signs, triangulations, Eulerian numbers" by Parisi, Sherman-Bennet, Williams - https://arxiv.org/abs/2104.08254.
"Positive geometries and canonical forms" by Arkani-Hamed, Bai, Lam - https://arxiv.org/abs/1703.04541.