I believe you are directly creating an email from existing marketing cloud template that's the reason you couldn't able to see the marketing cloud lock and properties.
Please follow the below steps to view all those:
- Go to
Content Builder > Click on Create > Email Template > From existing template > Select any one of the marketing cloud existing template
- If you hover over to any of the block , there will a downwards arrow > click on that and go to properties.
You have an wide range of options here.
Content Design assistance - Here you can specify what text you want to give. Like you have mentioned in your question (Pre-header, header etc..)
Max Number of Blocks - Here you can define in one content are how many number of blocks can be added.
Types of block - You can select what type of content block can be added or restricted. By just checking or un-checking the check box.
In the same screenshot you can see the 'Lock' where the content area will get locked. Once you are done with all your changes, you can save this template and create a new email on top of this template.
If you want to create a new template from HTML itself and not using any of the marketing cloud default template. Then you can add a HTML to create a content area like the below code:
<div data-type="slot" data-key="7vw3fh87g7t" data-label="Drop blocks or content here" data-max-blocks="1" data-allowed-blocks="freeformblock; htmlblock; textblock; abtestblock; dynamicblock; enhanceddynamicblock; layoutblock; imageblock; imagecarouselblock; icemailformblock"></div>
Let me know if this helps.