Cellulose in nanostructures is the most significant ecologically friendly resource globally and the most plentiful renewable polymer source. Cellulose possesses numerous desirable characteristics, rendering it an inexhaustible source of raw materials. The kind of lignocellulosic biomass and the method of processing affect the range of cellulose allomorphs. A novel substance, nanocellulose originates from the essential natural polymer cellulose. It possesses unique properties and functionalities such as sustainability, nontoxicity, renewability, a high area of a specific surface, good modifiability, tunable surface features, and exceptional optical properties. Various types of nanoscale cellulose can be generated by isolating cellulose fibers according to their origins, degree of crystallinity, extraction method, and production process. This review concentrates on nanocellulose and its most current applications. Begin with a basic overview of cellulose, its origins, and the many forms of nanocellulose and its sources. Finally, the review overviews the most recent advances in many nanocellulose applications, such as water treatments, heavy metal sensing, environmental remediation, and biosensing devices in many fields, including medical diagnostics and bioimaging applications.