Yes, there is a descriptive section in the SBI PO mains exam. This section is designed to test the candidate's writing ability and communication skills. The syllabus for the descriptive section includes:

Essay Writing:
Candidates are required to write an essay on a given topic. The topic can be from various fields such as social issues, economic issues, technology, environment, etc. The essay should be well-structured, coherent, and should present a clear and logical argument.

Letter Writing:
Candidates are required to write a letter on a given topic. The topic can be formal or informal, and candidates should be able to express their thoughts effectively in the letter. Formal letters can include topics such as complaint letters, application letters, etc., while informal letters can include topics such as congratulatory letters, thank-you letters, etc.

Precis Writing:
Candidates are given a passage and are required to write a summary of the passage. The summary should be concise and should capture the main ideas and key points of the passage. Candidates should also maintain the overall structure and coherence of the passage while writing the precis.

Paragraph Writing:
Candidates are given a topic and are required to write a paragraph on it. The topic can be from various fields such as current affairs, social issues, etc. Candidates should be able to express their thoughts clearly and coherently in the paragraph.

Tips for Descriptive Section:
- Understand the topic and brainstorm ideas before starting to write.
- Maintain a proper structure and coherence in your writing.
- Use appropriate vocabulary and grammar.
- Proofread your writing to check for any errors or mistakes.
- Practice writing essays, letters, precis, and paragraphs to improve your writing skills.

In conclusion, the descriptive section in the SBI PO mains exam tests the candidate's writing ability and communication skills. It includes essay writing, letter writing, precis writing, and paragraph writing. Candidates should practice writing and work on improving their writing skills to perform well in this section.