The Observing Tool (OT) is used for all Cycle 4 proposals and is thus very general. One of your first actions should be to choose the Sun as source because it will remove all irrelevant boxes and fields in the OT, greatly simplifying the proposal preparation. Start in the proposal section and select a regular proposal in the Scientific Category Stellar Evolution and the Sun.
Then choose the Sun as source in the Science Goal section (under Planned Observing):
Science Case document
From the Proposer's Guide, Sect. 6.2.1:
"The recommended breakdown is 2 pages for the science case and 2 pages for figures, tables, and references, but proposers are free to adjust these numbers within the overall page limit. Large proposals are allowed an additional 2 pages to describe the management plan and data products. Figures and tables may be interleaved with the science case, so that they appear close to the location in the text where references are made to them. Although the Technical Justification for each Science Goal is entered in the OT, any figure required for it needs to be placed in the Science Justification PDF document. Users are encouraged to use the LaTeX template developed by ALMA for preparation of their proposals (available at http://almascience.org/documents-and-tools/cycle4/alma-proposal-template).
A file size limit of 20 MB will be enforced at submission. Proposals must be self-contained. Their assessment will be based solely on their explicit contents, and no external references will be considered. Reference can be made to published papers (including astro-ph preprints), as per standard practice in the scientific literature. Consultation of those references should not, however, be required for understanding the proposal."