Refine backend doc (#7595)

docs/en/setup/backend/ttl.md

 # TTL
-In SkyWalking, there are two types of observability data, besides metadata.
-1. Record, including trace and alarm. Maybe log in the future.
-1. Metric, including such as percentile, heat map, success rate, cpm(rpm) etc.
+In SkyWalking, besides metadata, there are two types of observability data:
+1. Record: Includes trace and alarm. Log may also be included in the future.
+1. Metric: Includes percentile, heat map, success rate, cpm (rpm), etc.
 
-You have following settings for different types.
+These are the settings for the different types:
 ```yaml
     # Set a timeout on metrics data. After the timeout has expired, the metrics data will automatically be deleted.
     recordDataTTL: ${SW_CORE_RECORD_DATA_TTL:3} # Unit is day
     metricsDataTTL: ${SW_CORE_METRICS_DATA_TTL:7} # Unit is day
 ```
 
-- `recordDataTTL` affects **Record** data, including tracing and alarm.
-- `metricsDataTTL` affects all metrics, including service, instance, endpoint metrics and topology map metrics.
+- `recordDataTTL` applies to **record** data, including tracing and alarm.
+- `metricsDataTTL` applies to all metrics, including the metrics for service, instance, endpoint, and topology map.

docs/en/setup/backend/ui-setup.md

@@ -5,7 +5,7 @@ SkyWalking UI distribution is already included in our Apache official release.
 Startup script is also in `/bin/webappService.sh`(.bat). UI runs as an OS Java process, powered-by Zuul.
 
 ## Settings
-Setting file of UI is  `webapp/webapp.yml` in distribution package. It is constituted by three parts.
+Settings file of UI is  `webapp/webapp.yml` in distribution package. It has three parts.
 
 1. Listening port.
 1. Backend connect info.

docs/en/setup/backend/uninstrumented-gateways.md

@@ -2,12 +2,12 @@
 
 The uninstrumented gateways are not instrumented by SkyWalking agent plugin when they are started,
 but they can be configured in `gateways.yml` file or via [Dynamic Configuration](dynamic-config.md). The reason why they can't register
-to backend automatically is that there're no suitable agent plugins, for example, there is no agent plugins for Nginx, haproxy, etc.
+to backend automatically is that there're no suitable agent plugins. For example, there are no agent plugins for Nginx, haproxy, etc.
 So in order to visualize the real topology, we provide a way to configure the gateways/proxies manually.
 
 ## Configuration Format
 
-The configuration content includes the gateways' names and their instances:
+The configuration content includes gateway names and their instances:
 
 ```yml
 gateways:
@@ -17,6 +17,6 @@ gateways:
        port: 9099 # the port of this gateway instance, defaults to 80
 ```
 
-**Note** that the `host` of the instance must be the one that is actually used in client side, for example,
-if the instance `proxyA` has 2 IPs, say `192.168.1.110` and `192.168.1.111`, both of which delegates the target service,
+**Note**: The `host` of the instance must be the one that is actually used at client side. For example,
+if instance `proxyA` has 2 IPs, say `192.168.1.110` and `192.168.1.111`, both of which delegate the target service,
 and the client connects to `192.168.1.110`, then configuring `192.168.1.111` as the `host` won't work properly.