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Galaxy clusters are important cosmological probes since their abundance and spatial distribution are directly linked to structure formation on large scales. The principal uncertainty source on the cosmological parameter constraints concerns the cluster mass estimation from mass proxies. In addition, future surveys will provide a large amount of data, requiring an improvement in the accuracy of other elements used in the construction of cluster likelihoods. Therefore, accurate modeling of the mass-observable relations and reducing the effect of different systematic errors are fundamental steps for the success of cluster cosmology. In this work, we briefly review the abundance of galaxy clusters and discuss many sources of uncertainty. Os aglomerados de gal\'axias s\~ao importantes sondas cosmol\'ogicas, j\'a que a abund\^ancia e a distribui\c{c}\~ao espacial desses objetos est\~ao diretamente ligadas \`a forma\c{c}\~ao de estruturas em grandes escalas. A maior fonte de incerteza nas restri\c{c}\~oes de par\^ametros cosmol\'ogicos \'e origin\'aria das estimativas das massas dos aglomerados a partir da rela\c{c}\~ao massa-observ\'avel. Al\'em disso, os pr\'oximos grandes levantamentos fornecer\~ao uma grande quantidade de dados, requerendo uma melhoria na precis\~ao de outros elementos utilizados na constru\c{c}\~ao das verossimilhan\c{c}as de aglomerados. Portanto, uma modelagem precisa da rela\c{c}\~ao massa-observ\'avel e diminuir o efeito dos diferentes erros sistem\'aticos s\~ao passos fundamentais para o sucesso da cosmologia com aglomerados. Neste trabalho, fazemos uma breve revis\~ao da abund\^ancia de aglomerados de gal\'axias, e discuss\~ao de diferentes fontes de incerteza., Comment: 9 pages, text in Portuguese. Proceeding do evento As Astrocientistas: I Encontro Brasileiro de Meninas e Mulheres da Astrof\'isica, Cosmologia e Gravita\c{c}\~ao. Realizado remotamente entre 08 e 11 de fevereiro de 2021. https://astrocientistas.wixsite.com/astrocientistas

We are experiencing a period of extreme intellectual effervescence in the area of cosmology. A huge volume of observational data in unprecedented quantity and quality and a more consistent theoretical framework propelled cosmology to an era of precision, turning the discipline into a cutting-edge area of contemporary science. Observations with type Ia Supernovae (SNe Ia), showed that the expanding Universe is accelerating, an unexplained fact in the traditional decelerated model. Identifying the cause of this acceleration is the most fundamental problem in the area. As in the scientific renaissance, the solution will guide the course of the discipline in the near future and the possible answers (whether dark energy, some extension of general relativity or a still unknown mechanism) should also leverage the development of physics. In this context, without giving up a pedagogical approach, we present an overview of both the main theoretical results and the most significant observational discoveries of cosmology in the last 100 years. The saga of cosmology will be presented in a trilogy. In this article (Part I), based on the articles by Einstein, de Sitter, Friedmann, Lema\^itre and Hubble, we will describe the period between the origins of cosmology and the discovery of Universal expansion (1929). In Part II, we will see the period from 1930 to 1997, closing with the old standard decelerated model. The Part III will be entirely devoted to the accelerated model of the universe, the cosmic paradigm of the XXI century., Comment: 18 pages, 10 figures. To appear in Revista Brasileira de Ensino de F\'isica (in Portuguese)